[thena]

growth is very slow, nitrates are about 10-20ppm, has all this gray fuzz on it, what is it and how to i get rid of it

 

[Boredomb]

Pics not very cleat but it kinda looks like detritus.

 

[rsskylight04]

Might be brown algea. Look up images for brown algea online and compare to your tank. If it is brown algea then its harmless and will likely disappear on its own as it is out competed by cyanobacteria and green algea.
A better photo would help a lot.
Good luck!

 

[Flear]

detritus, diatoms, green dust algae, ...

those are my guesses,
it looks to be on the older leaves predominantly, ...

if it's any of those, ignore it and the problem will disappear on it's own
well detritus is a maintenance thing