Fish dying after filter change

[ludivine]

Hi, I have a 135 litre tank which had an internal liftech sponge filter but recently died. I also had a bad case of black/green moss.

I bought an external Resun filter and also used Algaecure according to instructions which was about one month ago & since then abou 6 fish have died.

I checked my PH levels & ammonia levels which are both fine. The water is clear and the algae has improved but I keep losing fish every couple of days.

Any suggestions on what may be causing this? It's really depressing.

 

[TKOS]

What are your exact readings in the tank. "Fine" doesn't really tell us anything. If you are lacking test kits most fish stores test water for free.

Generally the changing of filter media can result in an ammonia and nitrite spike as you loose a lot of good bacteria everytime you do that.

Also what exactly is in the tank? Fish, decorations, plants, heater, substrate?

Everything you tell us can help us come up with a better response.

 

[ludivine]

My ammonia level was zero and my ph levels were normal at 7.0.

In my tank now I have a heater, air pump, a rock and some fake plants with gravel at the bottom.

The fish I have include ghost knife fish, brown algae catfish peppered catfish, sailfin mollies, balloon mollies. At first when I put the filter in, the fish kept coming up for air, which is why I then went & bought an air pump & an accessory which pumps out bubbles.

I also have a hose with holes along it which is perpendicular to the water to aerate the water.

Sorry if I sound vague but I'm new to all of this.

 

[TKOS]

What is your water source? What are you using to dechlorinate with? You should check with your local water company or see if they have a website. Find out what is added to the water. Perhaps chloramines are added to the water.

It is rare that you need that much extra bubbling to get oxygen into the water. So if they are fighting to breathe then it can generally mean too much chlorine in the water or too much nitrite. So it is also important to find out what your nitrite level is (not nitrate, though that is good to know as well).