Slime algae

[jetjock]

Went out of town and turned off the ac. House must have got a little warmer than normal and so did my tank water. Now I have this purple/reddish alge on the gravel. Everything else is fine. I keep vacuming the gravel during water changes to get it out but it is back in 24 hours. Any suggestions would be appreciated.

 

[mojoreef]

Sounds like cyanobactor. Its presnce is telling you that you have some excess nitrogen (nutrients) in the gravel. Allowing it to suck it up is a good way of exporting the nutrient from your tank. You can try to get a little deeper on your syphon to get the material that is actually causing the bloom
Mike