Brown Stringy algae

[akarusso]

I have a 90 gallon reef tank with 90 pounds of live rock.
A month ago at my last water change I added a check valve to the retrun.

I noticed the tank getting dirty and the brown stringy algae.
Yesterday I removed the check valve and added a different one.
The flow is now more powerfull than it was there is alot more water coming out of the return.
Do you guys think the lack of flow for a month caused the brown stringy algae?
I have 2 clowns a yellow tang and a yellow wrasse.

 

[akarusso]

I also did a 15% water change.

 

[ZBT3091]

how long has your tank been running for? it could be diatom algae -- caused by water problems. any pics?