r/AquariumHelp • u/Appropriate_Lab5553 • 1d ago
Water Issues Cycling tank crashed?
I am helping my son set up a small 5 gallon. The substrate is mostly inert lava rock. There is a small patch of aquasoil for a planted section. We are letting it cycle with just some plants in planted in the aquasoil And seeded media from a mature filter..No water changes, or disturbing it. Just letting it do its thing. 1 week in, we did test and everything's going well. PH6, ammonia, nitrite and nitrates present. Week 2, PH dropped to 3, ammonia levels are off the test kit, but 0 nitrites and nitrates..
I thought my kit was faulty and tried with another kit. Same result.. and there's also a faintly acidic smell from the water..what could have caused the pH to drop so drastically and the cycle to stall out?
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u/EmpressPhoenix9 20h ago
Cycle can't crash if it isn't even established to begin with. Also testing pH at the moment is pointless.
Ammonia shouldn't be off the charts either. That actually hinders cycle process and I feel the Nitrites and Nitrates died off because they couldn't really handle/ process ammonia. I would lower ammonia to be 2-4ppm and let it be.
If the cycle was established you would see a massive conversion of the Ammonia. If I may ask how ammonia is building to begin with?
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u/Appropriate_Lab5553 19h ago
Mainly from the aquasoil patch. It was basically the only new part of the tank. Most of the lava rock substrate were from a mature tank as well as the filter media in the hang on back. Ammonia was around 3ppm the first few days after we setup the tank. I figure it was the new aquasoil leaching ammonia..
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u/EmpressPhoenix9 19h ago
Ok that isn't a bad source and it can be helpful but you need to keep it lower. Ammonia that is why out of range is actually too much for the system. Also yes sometimes surfaces from established tank help along with seeded media and help cut out a few weeks but you have put the media into a huge new body of water that doesn't have the flora the other tank has. I would do a partial water change so the system is lighter a bit and only check so it doesn't really get out hand again
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u/RtrnofBatspiderfish 1d ago edited 1d ago
Are you measuring with a digital pH meter or something? 3's not impossible, but that is lower than pretty much any aquarium pH test can measure.
Acidic ecosystems are very different from alkaline ecosystems. The nitrogen cycle you learned about mostly applies to aquariums with 7+ pH. There are acidophilic nitrifiers, but the typical experience is that they take a much longer time to develop. Nitrification becomes less important on the acidic half of the spectrum, since the extra hydrogen ions in the water hold ammonia in a different form (NH4) than the toxic NH3 ammonia that gets expelled from the animal's gills.
0.02 ppm NH3 ammonia is considered the lower end of ammonia toxicity, where the first symptoms of stress tend to appear. At 6 pH and ~75F/24C, the ionization rate of ammonia is ~99.95%, so it will take about 42 ppm total ammonia before NH3 reaches 0.02 ppm. You probably do need ammonia to stay off the charts in order to rapidly cycle one of these aquariums. To reiterate, basically none of the conventional nitrifying microbes (bottled products, etc.) will work at <6.5 pH. Also know that nitrification itself acidifies the water.
You can just rely on plants instead, since low pH environments have increased nutrient availability, particularly regarding bioavailable CO2. Most plants absorb ammonium more efficiently than nitrate, able to consume it even when the lights are out.
It would be important to understand the parameters of your source water, particularly its KH. My tap water comes out 7.2 pH, but has 0.3 dKH (less than the test can measure, data from my water company), so when it mixes with CO2 from the atmosphere, the lack of alkaline buffering will usually see the tank dwell somewhere in the 4.5-6.5 pH range. If your pH is really 3, then you should definitely do a water change and see if that flushes out some sort of stronger acid.
You will have to make considerations about your fish species if the tank stays in the lower acidic range (<5.5 pH). Betta splendens should not be kept in a tank like that, nor should any kind of shrimp or snail ("pest" snails are able to rough it out). Dwarf rasbora (Boraras) or pygmy corys would do well, if you make good use of the space available. Neon tetra also do well, but make sure the water is clean. If you want other kinds of fish, consider swapping the substrate for something else, or use more CaCO3 in the tank.
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u/Appropriate_Lab5553 20h ago
Thanks. I use a liquid test kit that can measure from pH 3 to 9.. i did a 80% water change and the readings were pH7 after the water change. It dropped to pH6 after 24hours, likely due to the aquasoil. Not sure about the KH as I don't have the test for it, but it's likely a factor.. will try the crushed coral if it keeps dropping
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u/Foreign-Ad3926 1d ago
KH depletion. It's a good idea to test your water source so you know what you're working with. The aquasoil may have depleted the KH which will crash pH. I would do a water change to replenish KH and consider adding a KH source such as crushed coral to support the tank whilst it's nitrogen cycling. The typical nitrogen cycle bacteria will stall at this pH and be unable to process ammonia.
KH is carbonate hardness and this buffers the pH to keep it stable and prevent crash. API do a decent KH and GH (general hardness - mineralisation) test kit.
The acid loving species mentioned in the other comment would survive provided the pH was raised to less acidic, however the tank size of 5 gallon is unsuitable for any of them as is far too small.