struggling to solve new tank problem


Help my dying Mollies: struggling to solve new tank problem

I have learned more since I started to read this site last night than all the answers I received from our local fish store.

Very frustrating! we set up our tank as per their directions and then bought 15 fish for our 20 g tank on day 6. 12 died over the first week. now in week 2 they said we need air stone, and antibiotics and sold us 4 more fish.

We changed 25% of water both yesterday and Monday. Should I continue with meds? or wait out the cycle?

the remaining 2 mollies from our first batch have been struggling for the past 2 days . very slow, inactive....I think they might die but they are hanging on.

Bought a test kit today: ammonia 0.1 - Nitrites 3.3
kit said to change 25% of water and replace with treated water=done at lunch time.

Just retested water and nitrite still at 3.3 ....what to do?

the test sad using some aquarium salt in recommended dose can reduce the nitrite levels.??

I am very confused and worried. the guppies and tetras that dies last week had the ragged tail fins. I can't see that on the mollies but they are listless and lying on the tank floor. - it is heartbreaking to watch.
the newer fish from Monday are fine so far.
Is there anything else I should do for the mollies?
please advise


you are still in the cycle of your tank, you need to do partial water changes everyday.. and if I were you I'd look into getting some tetra safe start, I personally have never used it but have heard nothing but great things on here. research the nitrogen cycle here... get a full explanation, plus when stocking a tank add fish slowly not all at once.... hope this helps


Stop adding more fish, that would be more than 200% of fish the tank could handle even if cycled already. It's not your fault, many lfs employees and chain employees give out BAD advice. Mollies are quite hardy, hence they are still alive. You only want 2 or 3 fish if you are doing a cycle with fish. Guppies and tetra are very sensitive to water conditions, even in a cycled tank. DO NOT use antibiotics or any medication in a new set up.

I don't want to bombard you with info and scare you away from fishkeeping, if I were in your position I would return all but 3 mollies to the store, wait around a month for the tank to cycle, then slowly add up to maybe 15 to 20 inches of fish in total. Good luck, hang in there. Get some prime or similar product to condition the water; do 25% daily water changes; the less chemicals you mess with the better. In about a month or so your tank will be healthy. (Sorry to tell you this but even IF any of the current fish make it through the cycle, at that amt of fish in a new set up, don't be surprised if the fish all die. Even after the cycle. Irreversable damage is usually done during a "fish in" cycle).

Oh, and welcome to FL. There are a LOT of friendly, helpful, intelligent fish keepers on this site - don't be afraid to ask, ask, ask questions. And don't ask the guy at the store you have been going to. *edit* I just noticed you have loaches as well, NEVER add salt to a tank with loaches, they have no scales and the salt will burn their skin and kill them.


Good info above. I have to agree stop adding fish until the tank has cycled. And to keep the rest of your fish alive use prime it will detox the water of ammonia for 24hours turning it into harmless ammonium. But after 24hours do a 25% water change and redose the tank with prime. Things should smooth out.

*Edit, ok...let me add this. If the rest of your fish die..get something much more dourable like tetras. Using the prime will keep then alive and they'll cycle the tank for you. Then like Morgan111 said add one fish at a time after cycling to give the bacteria a chance to catch up. Unless its small schooling fish then 5 at a time will be good.*
  • Thread Starter


just checked and mollie covered in either lice or cotton

thanks for the replies.

does that mean there are parasites in the tank? or is it a reaction to simply dying because of high nitrites?


High nitrites and ammonia. Don't be too concerned about parasites/medications.


at this point just be focused on doing daily water changes, dosing with prime or amquel+, you want to keep the ammonia (and nitrite) level as low as possible, and the best way is through dilution. Prime or amquel+ will condition your water, removing chlorine/chloramine, as well as detoxify the ammonia in the tank. Having ammonia in the tank is inevitable, it comes primarily from fish waste and decomposing food, but your purpose in changing the water and dosing with prime or amquel+ is to keep those levels as low as possible until the beneficial bacteria build up and are able to break the ammonia (and then nitrites) down on their own.(i.e. nitrogen cycle)
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