Misterious disease?

Question
I have a 55 gal fish tank. It holds about 30 small fishes (Glo, Tetra, Molly, Platty, Danio, Gupy & Pleco).

a couple of weeks back, I noticed some white dots on a black platy. He started attacking a molly balloon which, prompted me to separate them.
About that time, I noticed a few fishes missing, so took all ornaments from my aquarium and thoroughly cleaned up the bottom of the aquarium (which I now know I shouldn't have done that#, but I did find the decomposed body of the 3 missing neons.

The problem is that since that time, I lost steadily most of my fishes. And between replacing them and trying to maintain them alive, I fear something is wrong in my water.

I test id daily, and also took samples to 2 different pet stores and they all say my water is fine.

I've added Aquarium salt to the water, Conditioner & biologic filtration booster. My water temperature is abut 78 degrees. I don't have any fishes with white spots anymore #both platy & Molly died and have been since replaced).
I have bought 3 plants in a desperate move to see if it helps any, and I don't know if it is a direct result, but my water became cloudy...

The main question is how can I find what is wrong with my aquarium? Should I let everything die and start all over???

note: One odd thing through all this, is that I have now about 11 baby fishes that are alive and well...  

Answer
Hi Roni,

Those small white dots were most likely Ich (Ichthyophthirius multifilis), which is a common freshwater parasite. As the parasite went unchecked, you lost some some of the fish. Dead fish decomposing foul up the water quite quickly with toxic ammonia. However, Neons are small fish, and it would be extremely difficult to find them.

By completely cleaning out your aquarium, you may have gotten rid of the parasite. Unfortunately, this most likely depleted most, of not all, of the beneficial bacteria that live in the aquarium. These bacteria convert toxic ammonia (from fish waste) into less harmful substances. You've been adding more fish since you cleaned out the tank, which meant that the already small population of beneficial bacteria living in the tank cannot deal with the increased load. Therefore, the toxins in the aquarium increased and poisoned some of your more sensitive fish.

As you added biological boosters, the water may have become clean, and that's why the tests showed up good. However, there's no doubt that before the tests, at one point or another, there was an increased concentration of ammonia. Depending on the pet store, they may have tested for only one thing (generally pH) or more aspects (Ammonia, Nitrite, Nitrate, etc.)

The cloudy water is due to a bacterial bloom. The bacteria are now establishing themselves. The water can be cloudy up to a week, but normally clears up within a few days. This is a normal sign.

I'd recommend that you change about 10% of the aquarium's water daily for a week or so, until everything establishes itself. Remember to add water conditioner after every change. Keep on the look for any re-appearance of those nasty white dots. If they appear again, you'll need to treat it with an anti-parasite medication available at you local fish store.

You definitely should not let everything die and start over again. It's a painful process and not worth the time nor the lives of the current fish in the aquarium.

Congratulations on the baby fish! I'm happy to hear that your aquarium is well on its way to becoming the centerpiece of your home again.

Best of wishes,
Nathan

(You can email me further questions at nate4128@hotmail.com - I'm a bit busy to answer everyone's questions on this site, but I'd love to see how your aquarium turns out!)