fish dying in apparently good water, water quality checks out good. but....

[NickSeth]

hi there. sorry if i start a new thread by mistake, but i dunno how my problem falls in any off the others

i have a 30 gallon 2 feet tank (tall version) where i keep my community fishes and minimal plants

i have a few fishes that have been doing quite well for a long time and recently decided to introduce more plants as well as get a co2 set for my tank.

i got a new water monitor kit which monitors for chlorine and ammonia to try to predict when chlormaine mught form so it can be addressed

after adding a few more plants and the co2 set to my tank set up. i monitor my water quality very carefully. but my results have always shown there there is no chlorine present in my water, and with no, or little ammonia. so i take it that my water quality is fairly ok.

but after a few days... 2 of my penguin tetras died(on the same day) and these are one of my most lasting fishes.

the next day, 3 of my irnian(swallow-tails) died. and today, another irnian and 3 of my oriental swordtails died. but the water quality still checks out as ok. and the plants look alrite to me.

whats going on? wat should i do to remedy it? please help me soon b4 all my fishes die mysteriously

thanks

[Iggy]

Could something have accidentally been added to your water supply? It sounds a lot like poisoning?

Something you added, something on the plants (herbacide?)

Do a really big water change ASAP. Something is in the water that is killing them off.

[ducksarefun]

Is your tank cycled? I see you tested for ammonia, but what about nitrite and nitrate? How often do you do water changes ?

Chlorine is only a problem when you do a water change with water directly out of the tap. Leaving the water sit overnight will cause the chlorine to evaporate, or if you need to use the water directly, use a water conditioner such as stress coat. It will take out the chlorine immediately. Then you have no need to test for chlorine.

[FroggyFox]

You say you added C02 to the tank? have you checked for ph swings? When you add C02 to the tank it can drop the pH drastically...which of course would seriously stress your fish out.