RO Water for Aquariums

Changing pH, gH, and kH

If you are sure you need to use  RO water in your aquarium the first thing you must be aware of is that RO can’t be used “neat”. Fish need some minerals or trace elements to be healthy and thrive RO has virtually none.  Carbonates are necessary to prevent pH swings and enable filter bacteria to function.  You will have to put minerals and trace elements into the RO water to make it habitable.

Remineralising RO water by mixing with tap water

You can remineralise  RO water very simply by mixing it with tap water. You can halve the gH if you mix 50:50 RO and tap water together. Lowering pH is harder because the kH value needs to be considered. kH is what buffers the pH and if very high, pH may not reduce enough. If you keep fish that need very soft acidic water in a very hard water area, your mix may contain so little tap water that you will find using all RO plus minerals to be a better option.

Using 100% RO water with added minerals

Minerals can be added to pure RO water creating ideal conditions for the fish it will be used for. There are many products available: some are general mixes that raise both gH and kh, some raise only one or the other. You can also buy mineral mixes designed for certain types of fish: mixes for Discus, Rift Lake Cichlids, and others.

Hardness is more important than pH when it comes to remineralising,  and the most important factor is having the right TDS (total of dissolved solids) for the fish you want to keep. If you know the TDS you need you can use an all in one product such as TropicMarin Remineral Tropical or  JBL Aquadur for example.  All you need do is to mix enough of the product into your RO to reach the required TDS value using a TDS meter. The pH is less important in this method and all in one products add both gH and kH at the same time.

Where fish need either very low or very high alkalinity, separate products for gH and kH might be a better choice. Again there are many options including mixing your remineraliser from commonly available materials. Add remineralisers to your container of RO the day before a water change, with a heater and a powerhead to heat and aerate the water before use.

Vital Points  to consider when switching to RO Water in your aquarium

When you first switch to using RO you MUST do this gradually over a number of partial water changes. Changing hardness and/or pH too quickly is very harmful and can be fatal to some sensitive fish.

Once the change has been made you will need to continue with your new RO mix at EVERY water change. Suddenly going back to straight tap water is not an option. You will need to ensure you always have a supply of RO water and any minerals and adjusters to hand.

Your RO water mix must be consistent. Experiment and make notes until you can achieve the same parameters every time. Until you can be sure of being consistent, don’t start adding your mix to the tank

Other Considerations

Using RO can be costly, time-consuming and requires a commitment to accuracy and to continued use. You can buy it from your local fish shop (LFS) or buy an RO unit to make your own. Both have drawbacks and benefits. If you only need small quantities for one tank, buying from an LFS might be the way to go. For larger quantities, installing your own RO unit will work out cheaper.

If you choose to make your own RO, as well as the unit itself you will need a TDS meter, suitable food-safe storage containers, a heater and powerhead for mixing minerals and raising the water temperature and a plumber to fit the unit unless you are confident with DIY plumbing.  The prefilters and RO membrane will need to be replaced regularly.

The amount of water sent to waste can be high – typically for every litre of RO produced, four litres goes to waste consequently on a metered supply this can add a fair bit to your water bill. You may need to inform your water supplier of your intention to install an RO unit and additional charges may be made for water drainage. You can be required to have a meter installed if you do not already have one.

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Fishless Cycling Guide

How to Cycle an Aquarium with Ammonia

You can start your fishless cycle 24 hours after you have set up your aquarium, filled with dechlorinated water and turned on the heater and filter.

Shopping List For Fishless Cycling

There are a few things you’ll need to buy to carry out your cycle. This looks like an expensive list, but most of the items listed will be needed irrespective of how the tank is cycled. The only extra is the purchase of a bottle of ammonia and the cost of that will be less than you would spend on extra dechlorinator when doing daily water change for a fish-in cycle, or a LOT less than the cost of treating fish for ammonia burns, nitrite poisoning, bacterial infections and so on that may well arise in fish introduced to an uncycled tank. Here is what you will need, apart, obviously, from the aquarium itself:

  • Bottle of household ammonia with no additives. This may be available at a local hardware store or is usually available on eBay or Amazon. The Kleenoff brand is suitable.
  • A liquid type aquarium water testing master kit including tests for ammonia, nitrite, nitrate and pH. Kits by API and Nutrafin are recommended. Paper test strips are not suitable as they are too inaccurate.
  • A syringe for dosing the ammonia, available from any chemist
  • A bottle of tap water dechlorinator/water conditioner
  • A small pot of fish food – preferably flakes
Getting Started

Fishless cycles are usually conducted using between 2 and 5 ppm of ammonia, dependent on how many and what types of fish you will be stocking. Choose your cycling level and stick to it throughout the fishless cycle. Don’t exceed 5 ppm as dosing higher than that will probably prevent the beneficial bacteria from growing. To get your fishless cycle underway, calculate how much water is in your tank. This will be the actual tank volume minus 10-20%  for the space taken up by sand, and decor. Underestimating volume is safer than overestimating because an overdose may stall the cycle. You can use the calculator below to work out how much ammonia to add to the tank.

Ammonia Dosing Calculator
Current ammonia level (ppm):
Desired ammonia level (ppm):
Water volume (litres):
Ammonia to add (ml):

Use your ammonia test to check the level is correct; thereafter test the ammonia level daily. After approximately 10 days bacteria should be growing and as a result, the ammonia level will be beginning to fall. The bacteria which “eat” ammonia consequently produce nitrite hence as the ammonia level falls, nitrite rises. You can use the calculator again to work out how much ammonia to add to bring ammonia  back up to your starting level whenever it falls to less than 1 ppm,

Ammonia will reduce faster as the cycle progresses and the level of nitrite will rise more quickly. Nitrite may appear to stick at the highest level on your test kit’s scale for a considerable time, but this is an illusion due to the test kit’s limited range. The reality is that nitrite may climb beyond the limit of the test thus, as a result, you may be unaware of nitrite starting to fall as the cycle progresses. Testing for nitrate from this point on will guide you because as nitrite reduces nitrate will rise.

fishless cycle aquarium illustrationFurthermore, when nitrite starts to be fall, you can add a few flakes of fish food in addition to continued ammonia dosing. This can help during this stage of the fishless cycle, probably because fish food contains additional nutrients which nitrite munchers seem to like.

How do you know when a fishless cycle is complete?

The cycle is complete when you can add a dose of ammonia and test results 12 hours later show 0 for ammonia and nitrite. At this stage nitrate will have risen to a very high level, therefore, you’ll need to do a large water change (maybe more than one) to reduce nitrates to an acceptable level for fish. It’s advisable to continue dosing ammonia once a day for a further few days just to be sure, then do a final water change and you’re ready for your first fish.

Every fishless cycle is different, but typically, an initial cycle on a new set up will take around about 4 weeks. Some take longer, some less time than that, especially if you can get hold of some filter media from a mature tank to kick things off. In conclusion, if you encounter any problems with your fishless cycle why not ask a question?

 

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What is Fishless Cycling?

What exactly is “fishless cycling” – well it has plenty to do with fish and nothing whatsoever to do with bicycles. For fish to survive in an aquarium,  there needs to be a way of dealing with their waste products and the toxins from them.  The way this is achieved is by a two-pronged approach: the use of biological filtration and regular partial water changes.

What is biological filtration?

Biological filtration in aquariums is carried out by certain types of naturally occurring bacteria which feed on the toxins generated by fish respiration, faeces, left over food, decaying plant material and so on. Fish excrete ammonia from their gills, and their solid waste decays, along with dead leaves from plants, uneaten food adding more ammonia to the water. These bacteria need somewhere to live with flowing, well oxygenated water at the right temperature and a source of ammonia. The sponges or other media inside aquarium filters provide an ideal home for nitrifying bacteria and once a filter is running in an aquarium and ammonia is present, they will colonise the filter sponges and start work.

aquarium-fish-keeping-nitrogen-cycle

Illustration of the Nitrogen Cycle

Beneficial bacteria feed on the ammonia, using it to grow and reproduce, and releasing another toxin, nitrite, in its place. Other bacteria feed on nitrite and convert it to nitrate, which whilst still toxic in large volumes, is considerably less harmful to aquatic life. This process whereby ammonia is converted to nitrite and nitrite is converted to nitrate is called the nitrogen cycle which is explained in more depth on this page.  To prevent too much nitrate accumulating, we must regularly change some of the water in our aquariums as well as establishing a biological nitrogen cycle. Without this, our fish would soon die from the effects of swimming in their own waste.

In the past, the nitrogen cycle was established using so-called “hardy” species’ of fish; one or two were added to a newly set up tank and the ammonia they produced caused the cycle to gradually become established. Further fish would be added every two weeks or so until the tank was fully stocked and cycled. At that time it was widely believed that fish were unable to experience pain so the only consideration was to choose fish able to survive the process whilst being exposed to ammonia and nitrite over several weeks. In more recent and more enlightened times we have come to understand that fish can indeed feel pain and that although “hardy” fish are able to survive the cycling period, they do suffer pain and discomfort, damage to their immune systems, long term increased susceptibility  to infection and a shorter lifespan. Once this was understood, fishless cycling became the preferred method.

How can I cycle a filter without any fish?

The answer to that question is quite simple: household ammonia is an ideal substitute for the ammonia produced by fish. By dosing the tank with ammonia in small amounts we can simulate the presence of fish and water containing ammonia will be readily populated by the beneficial bacteria needed to turn that ammonia into nitrite and then turn the nitrite into nitrate. Fishless cycling has numerous advantages over cycling with fish, all for just a couple of pounds to buy a bottle  of ammonia. The most obvious, and for me, most important benefit is that no fish are harmed using this method. Other benefits include:

  • The ability to add a full complement of fish immediately after the cycle is complete
  • Fewer water changes needed during cycling – these can be needed daily to protect fish if cycling fish in
  • Some time to learn the basics of tank maintenance and water testing before fish arrive
  • Time to add plants and allow them to establish
  • Time to carefully research which fish you want to stock at the end of the cycle

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What is Reverse Osmosis (RO) Water? Why Would I Use RO?

What is Reverse Osmosis Water?

Reverse Osmosis water (RO) is made by passing tap water through a semi-permeable membrane which allows water molecules through, but prevents solids in the water from passing through; the solids are rejected. An RO filter has two outputs; one which produces pure RO water with virtually no solids and the other which is “waste” water containing all the rejected solids.

There are usually at least three stages of filtration: water first goes through a sediment filter which removes large particles, grit and so on. The second stage is a high-quality carbon filter which removes with metals such as copper and chemical contaminants such as chlorine, chloramine, pesticides and other unnecessary chemicals. The RO membrane itself is the third stage. The initial sediment filter and carbon filter stages are essential to prolong the life of the RO membrane and to prevent damage to the membrane which would make it far less effective.

RO-filter-diagram-fish-keeping-aquariumsMarine fish keepers add a fourth stage after the RO membrane which passes the RO water through deionising resin (DI) to take the total of dissolved solids (TDS) down to absolutely 0. This is not usually needed for fresh water tropical and cold water aquarium fish as the water produced by a 3 stage reverse osmosis unit is usually pure enough. Some do go even further and add additional stages with finer sedimentation media or extra carbon stages  before the water reaches the membrane. The diagram on the right shows how a three stage RO unit filters the water.

All stages of an RO filter need to be replaced regularly. The sediment and carbon stages should be replaced at least every six months and the RO membrane should be replaced when it starts to allow more solids through, which you can check with a TDS meter. If a DI stage is used, this needs regular replacement as it retains the solids it removes and eventually becomes saturated and can’t absorb any more.

A standard three stage unit will reduce the TDS of the supplied water by around 95% or more. When this drops to 90% or less it’s time to replace the membrane.

Why is RO water used by fish keepers?

When tap water is filtered by reverse osmosis many undesirable elements are removed or greatly reduced in concentration providing virtually pure water with very low amounts of dissolved solids and  virtually no hardness or alkalinity. This makes it possible to provide a lower level of hardness or pH for fish, even where these levels are high in the original tap water. It also deals with excessive levels of nitrate, phosphate, heavy metals and chlorine in the water.

Do I Need to Use RO water?

The answer to this question in many cases is, “No”. Our tap water (in the UK), is usually perfectly adequate for fishkeeping as long fish are chosen that suit the hardness and pH of your supply and a suitable water-conditioner is used to neutralise chlorine, chloramines and heavy metals. There are some circumstances where using RO is essential or at least very useful:

  • Where your supply is too hard and/or too alkaline for the fish you want to keep
  • Where the supply has a very high nitrate level and you have fish that are intolerant of nitrate
  • Where you want to tailor water to a very precise level for breeding fish or for wild caught fish
  • If you keep multiple tanks, all needing different parameters
  • Where your water supply varies in its hardness/pH/nitrate level because your supplier frequently switches sources

If the only problem is high nitrates in your water supply, it may be more economical and less trouble to simply use a nitrate filter rather than RO water. Have a look at this article on nitrate control in the aquarium.

If the problem is that your water is too soft and acidic for the fish you want to keep you won’t need RO as pH and hardness can be raised very easily, but where they need reducing, RO is the only reliable and safe way to do it successfully.

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Dealing with Ammonia and Nitrite Spikes in Aquariums

How can the unthinkable situation of ammonia or nitrite being present in an aquarium which is already stocked with fish arise?

There are number of ways this can happen. The most common is poor advice  suggesting it’s safe to stock a new tank within days or even hours of its being set up. This is how tanks were cycled years ago when our knowledge of biological filtration and the effects of ammonia and nitrite on fish were very different to current understanding. Unfortunately, not everyone has caught up with newer findings and fishless cycling is still often not mentioned, or not recommended due to lack of up-to-date knowledge. If you and your fish are the victims of poor or outdated advice, you’ll be in a situation where the biological cycle hasn’t had time to become established, leaving fish swimming in ammonia and nitrite and at risk of pain, illness and death from their effects.

The second common way in which this can occur is when other factors cause the bacteria in an established aquarium filter to die off or fail to cope. Some ways this can happen include:

  • Something blocking the filter
  • A power cut of more than a couple of hours
  • Forgetting to dechlorinate tap water before using it for a water change
  • Use of certain types of medications used to treat illnesses in  fish
  • Consistent overfeeding of fish or failing to remove uneaten food and excess waste regularly
  • Death of one or more fish or other tank mates whose bodies are decaying somewhere in the tank
  • Overstocking or introducing too many new fish at one time

The third major cause of unexpected ammonia and nitrite spikes is “old tank syndrome”. This arises when aquariums are not given regular partial water changes and are simply topped up instead when water evaporates. Over time nitrates build up, carbonates deplete and the water acidifies. Testing the pH will confirm this, as “old tank syndrome” usually causes a gradual lowering of pH. When pH drops to a low level, below pH 6, the beneficial bacteria can become dormant or even die, with the result that ammonia and nitrite begin to accumulate and fish start to suffer. If you have very soft water with a low level of carbonate hardness (kH) this can happen quite rapidly and regular partial water changes are absolutely vital if you have this kind of water. One of the signs that a tank may be on the verge of “old tank syndrome” is when new fish are added and seem to immediately become unwell or die very soon afterwards when existing stock appear to be fine. This is because existing fish have become gradually used to the high nitrates and low pH, but new fish introduced from healthy tanks find it too much of a shock and rapidly decline as a result.

Prevention is always better than cure and ammonia and nitrite spikes can largely be prevented by fishless cycling any new tank before adding fish, keeping stock to sensible limits, being careful not to overfeed and by carrying out regular maintenance to filters with weekly gravel vacuuming and partial water changes. Testing levels of ammonia, nitrite, nitrate and pH on a weekly basis just before the water change should alert you to any issues before they become too much of a threat.

OK, so you didn’t do a fishless cycle, or your cycle has failed and your fish are dying.  What do you do now?
  1. If nitrates are not exceptionally high, immediately do a 50% water change with dechlorinated water warmed to match the temperature in the tank and then do a 25% water change every day until your tank is cycling (i.e. ammonia and nitrite are at zero).
  2. If “old tank syndrome” is the reason for the filter crash and you have excessive nitrate levels, start by doing two or three 10% changes over a few hours on day 1 and then move to 25% daily changes when nitrates have reduced. Too large a change initially would shock the fish. Test the water daily for ammonia and nitrite until the values are holding at zero for several days running. If levels are high, do an immediate extra water change
  3. .If at all possible, get some filter media from a mature tank and put it in your filter; just cram it in along with your own media. This will introduce a small amount of beneficial bacteria which will rapidly multiply..
  4. Keep good aeration in the tank both to help the fish a little and to oxygenate those beneficial bacteria.
  5. Avoid using medications, if at all possible, until the tank is cycling. Many commonly used medications can kill off beneficial bacteria. Your fish may well be affected by ich, fungus or other infections due to the stress of the ammonia and nitrite in the water, but the immediate priority is to establish the cycle and improve the water quality.
  6. If you can temporarily rehome your fish while you carry out a fishless cycle, that is the very best option – especially for more sensitive species such as Plecos, Corys or other bottom dwellers, Tetras, Rams etc.. Try asking your local aquatics store  to look after them until your tank is cycled (after all, chances are that they got you into this mess in the first place!).
  7. Live plants can use ammonia directly, so add some cheap aquatic plants to the tank, such as Elodea or Giant Vallis.
  8. Don’t feed your fish at all if your ammonia readings are high, and only feed bare minimum rations every other day until the tank cycles. This will cut down on the ammonia the fish produce. Since fish are cold blooded creatures and don’t need the calories of a mammal they can go for several days without food with no ill effects. Your fish may not be very hungry anyway so do be careful not to feed more than the fish can eat and clean up uneaten food immediately, before it rots and produces even more ammonia.
  9. Continue to clean the gravel of obvious dirt and uneaten food as normal to prevent additional ammonia forming, but don’t aggressively clean or change any filter media. If the flow slows and the filter is blocked, just clean it enough to unblock it, using water from the tank to rinse it.
  10. Buy a bottle of Seachem Prime. This is a dechlorinator which also “locks” free ammonia into a less harmful form and provides some protection for fish from the effects of nitrite. Use a double dose sufficient to treat the whole tank every day in the 25% water change. If you use Prime, buy a Seachem Ammonia Alert so you can see the level of just the toxic ammonia – most tests also react to the “locked” non-toxic form so will not give reliable readings while treating daily with Prime or similar products.
  11. Continue this regime of daily testing, daily (or more frequent if needed), water changes, treatment with Prime or similar and reduced feeding until ammonia and nitrite are consistently reading 0. When that happens, congratulations, your tank is cycling and the fish are finally safe.
aquarium-fish-keeping-nitrogen-cycle

Illustration of the Nitrogen Cycle

 

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Dealing with high nitrates in aquariums

What should I do if I have high nitrates in my aquarium?

The first thing to do if you have high nitrates in your aquarium is to find the cause. You can deal with most causes of high nitrates by simple changes to tank husbandry. Is your tank overstocked? Are you skimping on partial water changes? Do you skip cleaning waste from the gravel? Are you over-feeding ? For all of these, the solution to the problem is easily within your control.

How can I reduce nitrate levels in the tank if my water supply already has high nitrates?

High nitrates in tap water is a common problem in the UK. You can reduce high nitrates in tap water either by taking nitrates out of the water before it goes into the tank or you can make changes to the tank and filters to allow some nitrate reduction to occur inside the tank.

Mixing tap water with RO water is the straightforward option, especially for those who also need to reduce water hardness. It’s easy to calculate the reduction given by any mix ratio as the concentration of nitrates reduces proportionally: A mix of half tap water and half RO water will halve the nitrate level. You can buy RO water from many aquatics shops or you can install your own RO filter. RO water must be remineralised for use in a fish tank as it has none of the minerals essential to fish health nor buffering capacity and so has unstable pH. If you intend using RO please read these articles: What is Reverse Osmosis (RO) Water? – Why, when and how to use it and RO water in your aquarium – changing pH, gH, and kH
Another alternative is to use a nitrate reducing filter. This will remove nitrates from the water, leaving other aspects of the water chemistry untouched. These can either be permanently plumbed into your water supply, with their own tap or used in a temporary arrangement with a tap adapter as and when needed.

A third option is to fill a container with tap water a couple of days before a water change and run an internal filter filled with nitrate reducing media in the container. A heater can also be added if desired, to bring the water to the correct temperature for your tank.

Final Comments

Please remember that reducing nitrates by any of these methods can be useful where there is a real problem, but should never be used as a substitute for correct stocking levels, regular water changes, and proper tank maintenance.

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Is nitrate control really necessary?

Why are nitrate levels important?

Nitrate levels in aquariums need to be controlled as at high levels they compromise the health and well-being of the fish. This can eventually lead to bacterial and fungal infections, white spot, fin-rot and other diseases that take advantage of compromised immunity. High nitrate levels are often the cause of excessive algae growth too.

The level of nitrates tolerated without ill-effect varies from species to species, but as a general rule-of-thumb the level in the tank should be kept as low as possible: ideally below 40ppm. Some species have a particularly low threshold for nitrates – Fancy Goldfish need levels below 20ppm as higher amounts can cause buoyancy problems which are frequently mistaken for Swim Bladder Disease. Where fish have low nitrate tolerance, care sheets will usually indicate this.

Water should be tested weekly using an aquarium nitrate test to monitor the level so you can be ready to take appropriate action when levels rise.

How do nitrates get into the water?

Nitrates are the end product of the nitrogen cycle. Any aquarium with life in it will accumulate nitrates as a natural consequence of the filtering process. Standard filtration does not deal with nitrates and they must be removed by regular partial water changes. A typical freshwater aquarium with the correct amount of stock, efficient filtration and correct feeding will need a water change of around 25% every week to keep nitrate levels in check and to replenish essential minerals and trace elements in the water that have been consumed by the tank’s occupants and plants.

Nitrates are usually present in the tap water used to fill the tank. The level varies with the source of the tap water, but in the UK must be no more than 50ppm by law. Most UK water suppliers provide information by postcode on various aspects of water quality for the locality, including the average nitrate level, but because this can still vary it is advisable to use your test kit to establish the nitrate level in your own water supply.

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The Nitrogen Cycle in Aquariums

What is the nitrogen cycle?

Understanding the nitrogen cycle is the most important stage in keeping healthy fish. When a new tank is first started up, we need to establish the nitrogen cycle to ensure toxins from fish waste are cleaned from the water and so cannot harm the fish. This means establishing a nitrogen cycle – or cycling the tank.

Simply put, fish excrete ammonia from their gills and as waste from their digestion. Solid waste also breaks down to form ammonia as does leftover food, decaying plant matter and so on. Ammonia is very toxic to fish so we need a way to remove it from the water to protect them from its effects. The filters in our tanks don’t in themselves do anything to deal with ammonia: they remove floating particles as the water circulates through them and they add flow and oxygen which are good for the fish, but a brand new filter won’t do anything about ammonia.

Biological Filtration

Filters contain sponges or ceramic balls or similar and water which contains ammonia attracts beneficial bacteria whose food source is ammonia. They will colonise the filter media and supplied with flowing oxygenated water passing through the filter, will extract ammonia from it and use it as food. As they do so, they produce their own waste product; nitrite. Unfortunately, nitrite is also very toxic to fish, but once nitrite starts to accumulate in the water, a second type of bacteria will also colonise the filter media and use the nitrite as food. These bacteria excrete nitrate, which is far less toxic than either of its precursors and won’t harm fish unless it’s allowed to rise to high levels. Nitrate is removed from the water by changing some of the water every week and replacing it with fresh water.

Because ammonia, nitrite and nitrate are all forms of nitrogen, we call this the nitrogen cycle.

aquarium-fish-keeping-nitrogen-cycle

Illustration of the Nitrogen Cycle

It takes quite a long time for the ammonia-eating bacteria to arrive and grow a big enough colony to deal with the ammonia in a new tank which leaves fish exposed to harm from increasingly toxic levels of ammonia for several weeks. Once ammonia starts being processed it takes another few weeks for the second type of bacteria to arrive and start processing nitrite, leaving fish exposed to high nitrite levels for that period. For these reasons, it’s no longer considered acceptable to use fish to cycle a tank and the correct way to do so is to fishless cycle, using a non-living source of ammonia instead.

Of course, many new fish keepers aren’t aware of fishless cycling and some still, unfortunately, find themselves with an uncycled tank having been poorly advised and so have to cycle with fish. If that has happened to you, you can reduce the fishes’ suffering and prevent their deaths from ammonia and nitrite poisoning by following this guide to dealing with ammonia and nitrite spikes.

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