Tank going through another cycle please help

[mdk2424]

Ok I had the tank set up since october went through the cycle in late december.
water conditions
amonnia 0
nitrites 0
nitrates 10 FOR SOME REASON NEVER GOT ANY HIGHER
ph 7
doing 5% water changes a week in a 29 gal tropical fish tank stocked with 18 fish all was good fish were happy and now there dying.
2 weeks ago ph droped to 6 and the next day amonnia .50 then every thing went down hill since.
amonnia 8
nitrites 0
nitrates 0
ph stll crashing 6 / 6.4
been doing 25/40% water changes a day to cut the amonnia down but nothing seems to be working. SEEMS LIKE I AM GOING THROUGH ANOTHER CYCLE BUT WHY????????????????????????????
Please and help or advise to save my sons fish would be helpful thank you.

[fins_n_fur]

I'm sorry that you having major issues with your tank...a few questions:

1. Have you done any major filter maintenance before the crash started? If so, what did you do, exactly.
2. Have you changed the brand of dechlorinator/water conditioner (if so, from what to what)
3. Have you introduced anything new to the tank?
4. Can you get a hold of tetra safe start or at least get some media from an existing cycled tank?

[tim k]

What are you using for a filter and have you cleaned it or the gravel?

Tim K

[Lady Hobbs]

Why only 5%. Water changes should be 25% and many of us do 50% and even more weekly. Fish pee in this water. Water needs to be replaced and replaced regularly. Always use dechlorinator unless you have well water. You will kill your cycle if you do not use it.

If you tank is dirty and has a lot of food laying in the gravel, it will also rot and needs to be vacuumed out periodically. This also causes high nitrates and I wonder if you happen to check your nitrates since you cycled? If your nitrates rose, this could have killed your fish.

Ammonia of 8 in a fish tank is impossible if there are fish in the tank. They can not survive those levels.

It could be that a fish or two died and was not removed and this rotting fish increased ammonia levels, as well.