Ammonia issues - shall I replace substrate (and nuke my pest snail infestation)

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Aquarium Advice Newbie
May 30, 2024
Hi there
I have been having ammonia issues (0.25-0.5) in our established planted 150litre tropical tank for about a month now. There is 0.5 ammonia in our tap water. To deal with this we have started waterchanging with RO water, but this hasn't made much of a difference. Our nitrates are also 20-30. Higher than normal for us. We have lost one platy so far with pine-coning. Relevant factors:
- madagascan snail infestation (literally hundreds) - could the dead ones be feeding the ammonia levels?
- Quite a lot of old food pellets are in the substrate because my hopplo sternum catfish hoards and doesn't eat them all. They are not siphoning up easily when I clean which I do on a weekly basis.

We are going to reduce the bio-load on the tank by getting rid of a lot of platys over the next 10 days, but in the meantime I am starting to wonder about changing the substrate completely - taking all the snails with it and euthanising the lot of them with clove oil.

Will a change of substrate cause huge additional problems? Advice very much appreciated because this is our first tank.

With thanks :)🙏
A significant amount of the microbes that are responsible for your cycle will be living on the substrate. Changing the substrate will remove these microbes and your cycle would need to catch up. Typically you don't want to change more than 1/3 of the substrate per week so you dont affect your cycle too much in one go.

Unless your substrate is leaching ammonia, i dont see how changing it will help with ammonia levels. Some substrates, in particular dirt based ones, might leach ammonia, but its usually only for a couple of weeks before its all leached out.

Are you remineralising the RO when you do your water changes?

Even if you did completely change out all the substrate, it wont help much with pest snails. They will be on your plants, in the filtration etc. Once they are in your aquarium its practically impossible to be rid of them short of starting over, sterilising everything etc. All you can really do is control overpopulation by not overfeeding, manually removing them when you see them, maybe an assassin snail. There are chemical treatments, but they will kill all invertebrates and you havent said if there are any shrimp or snails you want to keep.

If ammonia is elevated and not cycling out you should look at whether your filtration is sufficient. It might be that your system just produces more ammonia than your filtration is capable of removing. The ammonia in your tap water is from chloramine, but the levels of ammonia in chloramine should be cycled out in a matter of an hour or so, and wont be contributing too much to nitrate levels.

Its possibles dead snails are elevating ammonia, along with overstocking, over feeding, and having uneaten food. These are things to be looking for.

Your nitrate isnt that bad. Your plants need the nitrate, 30 to 40ppm is a good level for the health of your plants without it being harmful to your fish.
Firstly, thank you so much for replying! To answer your question, yes, I do reminilarise the RO water before I use it for water changes. I'm still stuck on where the ammonia is leaking out of, since I think the filtration is high enough, but I could be wrong. I have a fluval 207 external filter, and an eheim biopower 200, which I usually have both running at the same time.

My only concern, is that when I look down at the substrate during maintenance or when watching my fish, I can see lots of uneaten and decomposing food pellets, which must be from a long time ago when I used to overfeed. I also have found dead snails, and I'm considering, since our ammonia is at a constant 0.25, that the substrate could be the source of the ammonia.

Do you think it would be worth it, and safe, to remove the substrate partially over time? For example, removing and replacing one third of it first to see if that helps? We are also rehoming many of our platys next week, incase the bioload has become too high for the tank to manage.

Again, thank you so much for your help.
Just try something for me.

Do an ammonia test on your RO. Its not uncommon for an ammonia test shows a trace amount when in fact there is zero ammonia. RO should be zero ammonia, so if the test from your aquarium, and the test from your RO looks the same then your aquarium ammonia is zero.

Honestly though, 0.25ppm of ammonia is practically zero. Its just not worth worrying about that level, ammonia just isnt that toxic unless you have high pH and really warm water. Your pH would have to up in the high 8s and temperature above 30c for such small amounts of ammonia to be toxic.

Remember that fish are constantly producing waste, and that waste is only removed once its gone through your filtration. There will always be an amount of ammonia in your water. Usually this will be so small your testing isnt accurate enough to detect it, but for practical purposes, 0.25ppm and zero are the same. If there was a problem your ammonia would rise in between water changes rather than just stay at a constant low level.
I've read that the API test kit can give false readings of 0.25 when there's actually 0ppm ammonia. So if you're using API I wouldn't worry too much, especially at that level.
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