The nematodes are very small white wormy looking things..that move along the side of the tank...they squiggle alot when on the bottom of the tank. The white dots, not sure what they are, but I don't think they are harmful... <img src="/images/graemlins/confused.gif" alt="" /> ...if the betta see them moveing...they eat them!
Hhmm...however there are parasites that you have to be concerned about..like gill flukes..which look like stringy things coming from your fish's gills. Not a good thing..but if your fish aren't showing any signs of parasites..(and I'm not exactly sure just what 'ALL' the signs are..but wasting away is one and the stringy stuff in gills is another)..then I don't think you need to be concerned. Even healthy water has lots of weird crawly things in it that are too small to see...I don't think we need to worry about the ones you CAN see as long as the fish are healthy and don't seem to mind.
Having said that I remind all that I am NOT an expert on aquariums! Might be good to do some more research on those things. <img src="/images/graemlins/wink.gif" alt="" />
Emg <img src="/images/graemlins/cool.gif" alt="" />