Sudden Deaths :(

[Chou]

I keep a small, 5 gallon filtered tank in which I have kept a blue gourami, a loach, and a suckerfish healthy for nearly 5 years. Last week I went to PetSmart to make a new addition to my aquarium. I chose a dalmatian molly, which I noticed had small orange/red spots on its body when I brought it home. I slowly acclimated it to my tank, but it still behaved oddly and chose to hide all of the time ( I thought it was just shy ). But a week later, I came home to find my suckerfish dead. I emptied my entire tank and washed everything off in hot water before I put my fish back in the tank. Two days after the suckerfish died, I found the new dalmatian molly floating at the top of the tank.. I am wondering if the suckerfish died of old age, or if I brought home a contaminated molly from the pet shop. I can provide photos of the molly if needed. I would just really like to take the proper precautions to keep my other fish safe.

[Scuba Kid]

Well first off, your tank was overstocked. Thats a large bioload for a 5 gallon tank. Did you check your ammonia and nitrite levels when your suckerfish died? I'm assuming your "suckerfish" was a common plecostomous, which would grow far too large for a 5 gallon tank. If it was a common pleco and it fit into a 5 gallon, it did not die of old age. They can grow over 14-16 inches long.
Second, cleaning your tank with hot water is probably what killed everything else. Essentially, you killed most of the beneficial bacteria that consumed poisionous ammonia and nitrites formed from fish waste. This caused your ammonia and nitrite levels to sky-rocket and kill your fish.
Do you know about the nitrogen cycle? Itsthe process by which that good bacteria builds up to keep your ammonia and nitrite levels in check, along with regular water changes. I suggest reading the stickied post here about the nitrogen cycle. I believe its in one of the freshwater sections.

[Chou]

I didn't check the water levels..but I would hope they were fairly safe. I replace about 1/4 of my tank's water with bottled spring water every other week to keep it clean. I also only rinsed off the fake plant and little cave in my tank if that helps... I will be sure now to at least not make any new additions to my tank so that my gourami and molly have plenty of space

[Fresh Life]

Kepp replacing it with bottled spring water every once in a while, What I would do is Get your fish out and put them in a smaller tank for some time. Wash the tank and put Poland Spring in the tank. Let the filter run for some time. then check everything out. GoodLuck

[JustOneMore20]

Welcome to the site, Chou!

What I would do is Get your fish out and put them in a smaller tank for some time. Wash the tank and put Poland Spring in the tank

Putting the fish in a smaller tank is not going to help. The gourami and loach both need atleast a 30g tank to live comfortably and already may be stunted.

Washing the tank will make the situation worse. You already killed the beneficial bacteria when you rinsed with hot water. Your tank was overstocked, but was cycled after 5 years and had good bacteria built up to take care of the fish waste.

I'd get atleast a 20g tank as soon as you can, but I understand that the fish have been living in the 5g for quite some time. With the 20g, after it is cycled (which can take around 4-5 weeks), then you could add more fish safely.

I suggest buying a test kit that tests for ammonia, nitrite, and nitrates. You'll need these to monitor the cycle and to see when you need to do water changes to make the tank safer for the fish (lower the ammonia and nitrite levels).