stubborn toxic cloudiness

Sorry for the long post but I want to answer questions I know people will ask.
We just started a 47 gallon tank-- our second. After filling it with a mix of water from old tank and new water and cycling for a few days, we added one cichlid (trying to save it from agressive male) and the next day three mollies. The next morning the cichlid was dead, the mollies were barely alive, and the water was so cloudy I could barely see through it. The rocks were covered in a light film slimy to the touch. We removed all the fish and "shocked" the tank with chlorine. Emptied and scrubbed tank and all decorations, threw out plants, ran water through the gravel five times and refilled, began to cycle again. Water crystal clear for 24 hours, all chemical levels good (except for water hardness-- high-- which hasn't been a problem in our other tank). We put the three mollies back in and they seemed happy enough. This morning the tank was cloudy again and the mollies were all at the top, as if they couldn't breathe. We took them out again but are at a loss as to what to do next. We have a Fluval 350 canister filter with carbon, ammonia remover, and Biomax in it. Water is steady at 79 degrees. Help! I don't want to kill any more fish...

Hi, welcome to the forum! I am truly sorry to hear about your troubles. I think I have an idea what the problem is. You said you cycled the tank for a few days. Cycling is a process that normally takes weeks. It is likely your tank does not have the bacterial bioload to handle the fish you added to it and this has caused your tank to cycle all over again and do a bacterial bloom which has caused your cloudiness. As for what is killing your fish I am thinking it may be ammonia. This happens when a tank has not fully completed a cycle. There is not enough bacteria to handle the ammonia and break it down and the ammonia has been burning your fished gills. If you really want to have fish in your tank at this stage you would one need to do very large water changes every day which will only prolong the cycling process or you can get a hardier fish like a feeder goldfish to help speed things up. You can then sell the goldfish later if you do not want to keep them. When you do add fish you should be sure to test for Ammonia, Nitrites, and Nitrates. Any levels of ammonia and nitrites will harm or even kill your fish. Nitrates should be no more than 20 ppm. If do not have a test kit for these yet you can pick one up at your local fish store. Hope this helps some.

Welcome to myaquariumclub.com!

Adding to what Megan said, the good bacteria that help cycle a tank live in the gravel, plants, and decorations. Very few of them live in the water, so water from an established aquarium will not help near as much as a cup of gravel from it. Check some of the posts and blogs on this website for lots more details on the nitrogen cycle. A few commercial products are sold to speed up the nitrogen cycle, but I have no personal experience with them. Gravel, live plants and some flake food always seem to work just fine. No matter how you cycle your aquarium, remember to check for ammonia and nitrite before adding delicate fish.

And speaking of fish, cichlids and mollies are not a good mix. They require different water conditions, and cichlids tend to be aggressive.

Thanks for the welcome and the replies. You both had some great ideas and we're going to start again and implement some of them. I'll let you know if it gets any better or we learn anything new.

PS About the cichlid-molly mix, we have been told this. We got our first tank just to raise cichlids but they haven't acted like what we expected. While they're aggressive towards each other (why we moved one out) they haven't bothered the danios or the mollies at all. We had expected them to eat them (supposed to help cycle the new tank) but no, not even after they've had babies! Go figure...

Cichlids become more aggressive as they mature sexually. Some varities also get very large.

Many experienced aquarists keep single species tanks so they can provide the perfect conditions for a certain type of fish. I'm happy that you're doing some research and taking a careful approach to raising aquarium fish. People who are new to the hobby often get discouraged, because they experience losses from lack of good aquarium maintenance, over feeding, over crowding, and mixing species that have incompatible needs. It's usually best to start with some research and try the easy varities first.

Thanks again for participating in our forum.

Welcome to the forum!

Looks like they've already covered your questions.

Good Luck with your new tank.

After it's cycled... It'll be great.

I know that cichlids are sometimes very aggresive... I was reading an article in a magazine the other evening... I think it was TFH but I'm not positive about that... But it spoke of the impressive brain function of certain cichlids. If a bystander observes fights between other cichlids, it remembers which fish was the winner, and will challenge the loser. This is amazing!

Maybe Dianne will chime in, or you might PM her. She has a beuatiful cichlid tank.

Good Luck with your fish!