Probably diatoms, usually symptomatic of some combination of nitrate, oxygen
deficiency, and insufficient lighting. Recommendation: change water,
increase wattage and/or period of lighting, and add snails or ottos.

kush

Stuart Mueller wrote in message
. ..
I have a smattering of some brown fuzzy stuff over an area of my gravel.
it
is a patch in the centre. it looks like a fine build up of dirt. is this
algae? if so what sort?

Thanks

Stu