Brown 'algae'(?) Covering My Tank

[Spishkey]

ok i have a juwel rio which was set up for a year as a community tank. it never had a problem. then about a month back i put the community into a 500L and used the juwel as a crayfish tank.

now it contains a few red claws, 2 angels and 2 catfish. it has been a crystal clear tank up until last friday when i noticed brown patches appearing on the rocks and wood. by this morning the tank was COVERED in it, you could hardly see through the glass. i have spent the past 2 hours cleaning it.

now it didnt need to cycle as i kept the old media and it was swapped over from fish to crays within an hour or two. i cant understand what the brown stuff is or why its appeared now? my nitrates have risen from 5 to 15 but a large water change has been performed whilst cleaning.

the only addition has been a new female redclaw last weekend, could she have brought something in with her?

 

[minxfishy]

Sounds like typical brown algae, although if the tank has been set up for that long, its unusual, as it normally only occurs on newly set up tanks.

Did you change the substrate for new at the time?

 

[Spishkey]

yes i changed it from sand to gravel for the crays to dig in.

 

[minxfishy]

Could be from the gravel then, apparently brand new gravel can be a cause of brown algae, its just a case of wiping it off until it finallly stops, usually a couple of week.

Just to ask, how long do you have the tank lights on?

 

[Spishkey]

i dont have the tank lights on at all as crays like it dim, but there is a lamp above the tank which is on from 8pm until 6am (kids night light)