bugs?

Question
Hello. I have had a 10 gallon tank for about 2 years. This tank has always been healthy and I have never really had any problems with it. I had one male betta, a few small guppies, tetras and zebra danios. All the levels in the water were normal. I noticed about a week ago that my betta was laying at the bottom and when he would try to move, he would swim violently in circles. Almost like he had brain damage. This was heart breaking. :( Then the next day my tetras all died. They had no signs of disease, and were just found dead. Wanting to save my guppies and danios, i removed them and put them in a smaller aquarium. I looked long and hard at the aquarium water and noticed tiny little white bugs swimming in the water. They do not look like worms. I tried parasite medicine but it looked like they doubled in amount after I treated them. I have heard that they are harmless but then what is killing my fish? Can you please help me, i need to get this fixed so my fish can go home!! Thank you!

Answer
Dear Vanessa,
I don't believe it is the bugs harming your fish. These are likely little critters called Nematodes. These tiny creatures are harmless but can be a sign that your aquarium is polluted. How often do you do water changes?

Always insure that your ammonia and nitrite are ZERO and nitrate less than 20. Nevertheless I would start doing 30% water changes everyday until your fish look better. Make sure to vacumm the gravel well and clean the filter (in old aquarium water only) Do this everyday until your fish improve.
I would put the guppies and danios back into the aquarium as being in a smaller aquarium can cause harm to them if that small aquarium hasn't been cycled.

Water changes are the key here. Feel free to write me on any updates of how your fish are doing. I will be happy to help in anyway I can!

Best wishes,
Karen~