What causes Diatoms in established tank

[Swimmingwiththefish]

My tank has been up and running since March 2012. I started with a 55 gallon. In January 2013, I upgraded to a 75 gallon. I transferred existing sand, rocks, filters etc to the new tank. The only thing that was new was the water!

About 2-3 months ago I stared getting brown algae on the glass and rocks. It comes off easily with a good scrub brush. I'm assuming its diatoms, but seems unusual since my tank is not new. Any thoughts on why this is happening? Thanks.

 

[bobofishman]

Possibly a lighting issue bulbs do wear out and loose their lighting spectrum. Or you cleaned your tank to good ...try new bulbs.. I had this issue a few months back after I cleaned my tank to good .. It took some good water changes and not letting the algae float into the water by holding the siphon right against the area your scrubbing. I also added a placo once I noticed it wasn't growing back after a few day after a water change . Now I have no algae