i uploaded a pic and i dont know what it is. i have looked EVRYWHERE on the web and people have the same thing but its NEVER solved on what it is and how to get rid of it. It looks like mini transparent white trees all over the place and i mean EVERYWHERE!!!! its not hydra i know that because i have studied hydra in my zoology class. i have come to some sort of conclusion that it has to be some sort of rotifer or something. some of you hard core fish people had to of had this problem before. First help figure out what it is and how to KILL IT! Taking all the fish out of the tank is out of the question.

here is another pic i found on the internet.

had the same thing in my 10g and I put my Dalmatian molly fry in there and they ate them all.

I wouldn't worry too much.

Well, I had the same issue in my ten gallons tank. But mine has no fish in it. That thing were killing all my plants they are kind of spore so I high the temperature and also make a 75% of water to keep my beneficial bacteria alive. Also cut the air more to eliminate the oxygen a little to give the plants more C2O
Is works for me because got no fish in so got to be carefully when low the oxygen cause the fishes. Good luck.

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55 Gals. Plants Anubias,Amazon Swords and more. Tetras: 6 Sarpaes.4 Red Eyes,5 Black Skirts,4 Giant Danios,2 Lemons, 2 Emerald Cory,4 German Blue.
10 gals. tank : Plants, Full of Guppies; 20 Gals. Tank planted Full of Guppies: 1 gal tank filled with Guppies