freshwater red worms or fungus?

Question
Hi,

I have a 20 gallon freshwater aquarium, that had goldfish, red clawed crabs, 2 african dwarf frogs, and 2 algae eating fish. the tank is normally kept quite clean. recently one of the goldfish and one of the frogs were found dead, and beginning to decompose. the bodies were removed from the tank. then this morning (the following day), one side of the tank had several clumps of red, sporelike fungus/algae...and with a closer look it looks as though there are small red wormlike things "swimming" through the water. Can you tell me what this is, if its harmful, and how i can take care of this problem?

Thank you very much,

Todd Schurr

Answer
Hi Todd
Red wormlike things swimming in the water, sounds like it's most likely just nematodes.  Nematodes look like small tiny hairs, that look like an S when they swim in the water, usually they're white or clear, but I have seen some that were brown/reddish color-especially if the food you feed the fish is that color.  They're harmless  to the fish and fishkeeper.  It's also possible what you're seeing is bloodworms or tubifex worms, especially if you've fed live forms of those foods to your fish before.  Those are generally both harmless as well, though there has been some talk of I believe it was a parasite in the tubifex worms that can infect fish.

Usually you'll see large numbers of nematodes show up in a tank that the fish are being overfed and/or not enough water changes/gravel vacuums being performed.  They tend to reside in the substrate, and usually they're noticed when the substrate is disturbed.  They can be introduced into the tank through live plants or rocks from outside, live foods, even when you add the fish from the store especially if you dump the bag of water into your tank.  

Best way to take care of them, or cut down their numbers, be sure to do a good gravel vacuum at least once a week.  Cut back on feedings, only feed once a day(even skip a day or two during the week) what the fish will eat in a few minutes.  Net out any uneaten food, which can be a bit of a problem with your frog and other bottom dwelling critters in your tank since they can be difficult to feed. But, the fish and frog should also be eating those worms as well.  That's really the best course though for getting rid of them-increased cleanings and cut back on amount of feedings.

I see a few other potential problems in your tank though.  How many goldfish do you have?  A 20 gallon tank is really only suitable for one fancy variety of goldfish.  
And, what kind of algae eaters do you have?  Depending on the type, they may need something way larger then a 20 gallon.  Frogs generally shouldn't be with goldfish, reason being, African dwarf frogs don't see very well, and it's hard for them to compete with fish for food.  Usually they end up starving to death.  
As for the crabs, I"m not real familiar with them other then basic info, but I"d be hesitant with them and the frogs in the same tank.  
If you don't have a test kit, I'd recommend picking one up and monitoring your ammonia, nitrite, and nitrate levels.  Ammonia and nitrites should always be 0 ppm, nitrates under 20 ppm.  Especially if your tank is newly set up(within the last 3 months), your levels may be off.  And, they may be off as well depending on the size of the goldies and algae eaters.  I mention that, because that may be why your goldfish and frog died-from water quality.

Hope that helps and good luck!  Let me know if you have more questions.

Christy