in a fishless cycle - 20 gal tank - seems stuck in nitrite portions. found white stringy yuck on my plants. seems to disolve to nothing when I pull a piece out. but found a chunk of something white and disgusting floating in tank. Pulled it out and it is a soft mass, something like (please excuse me for this) a soft booger. can't seem to find anything like it online or in my books. Any ideas?