Hi all, I've a total 45 fish in my 2.5ft tank which is set up some 5 weeks ago. But in these past 3 days (including today), 7 fish has died (1 neon tetra, 1 black neon, 1 zebra danio, 2 guppies, 1 cherry barb & 1 ballon molly). Another guppy is dying too. I do weekly or fortnightly water changed (abt 30%). The last change was on last Sat. I started to feed the fish with frozen dried worms (in can) on Tuesday & the last time I added new fish (2 black neons & 2 molly) to the tank is on Tuesday & the 7 fish started dying on Wednesday (of course previously there were also fish died but the rate is not that high & close to each other). Does anyone know what seems to be the problem??

Too many fish contributing to high nitrates. Have you tested your water parameters with the test kits namely NO3, NO2 and Ammonia? Something has to be out of whack here. Also I'm sure your tank cycling was not complete before putting in fish. Nitrification doesn't happen overnight. Do you put any ceramic rings inside your filter and what kind of filtration? More specific information will be needed before anyone can help you here.

Too much nitrates? No wonder my plants are growing strongly rite? :O
I think I need to get some equipments in order to test the no3/no2/ammonia. Do I need to buy 3 separate testers for each type?

I'm using a hang-on filter which contains bio-rings, activated carbon & a sponge. When I chg the 30% water once or fortnightly, I will clean my filter as well by washing using the tap water. Am not sure whether this info is sufficient.

Now my tank is only left with 37, more than 15 have died since I set up my tanks 5 weeks ago. Is there a way to reduce the nitrate in a tank? If not, what could be the other causes of the high dead rate? I was told in another forum to chg 100% of my water as a last resort.

Hang on filters don't have much capacity for bio filtration. As it is your bioload can hardly keep up! Secondly, when you clean the filter by washing those rings you have just killed off most of the good bacteria. Therefore your nitrates will always be on high side. Yes, 3 separate test kits.

Thx. I think my water chg last Sat morning does help. There is no more fatality for the past 2-3 days. I think I'll chg water weekly instead of fortnightly. I think this is 1 of the cheapest way to control the nitrate level, rite? Also, maybe I should keep the number of fish in the tank to below 40.