Am I crazy?

[Mr_Cool]

I've been having a little problem with with a brownish, red algae or something growing on my sandbed. I'm thinking it could cyanobacteria or diatoms, but I'm not sure. I've been using RO/DI water, so I don't know where the phosphates or silicates could be coming from. Anyway, I see this brownish, red coating on my sand every night. It's not too bad. It only shows up in areas the the light really hits, too.

Here's the thing... I teach high school, so I'm on spring break now. :D So, I've seen the tank before the lights go on for the past couple of days and I swear that coating is not there. Normally, I take a look at the tank before I go to school, but it's still kind of dark outside and there are shadows in the tank, so I guess I never noticed. But the past few days, I've had time to look more closely. I just took another look now. It's 9:00 AM. The sun is shining. Corals are all starting to open up as the sunlight does a good job of filling the room. But, there is definately nothing on the sand. What's going on? Where did the brownish, red covering from last night go? Is this normal, or as the title says, Am I crazy?

[GaryP]

Something could be eating it. Some of the hermits will eat cyano. That sounds like what it is to me. Diatoms are sort of brown/gold color. Cyano makes a reddish mat.

Where is the silicates and phosphates coming from if you use RO/DI? That's real simple. Fish food. Food can contain 1% phosphate on a dry weight basis. The water in SA/Austin is actually very low in phosphates. The water quality reports from SAWS actually show them as being undetectable and I am sure their lab equipment is a lot more accurate then what we use. Silicates can come from phosphate removers such as Phosguard.

Cyano is common in areas with low flow, low oxygen, and that accumulate detritus and excess food. The areas near the base of the rockwork are usually prime areas for cyano growth. Diatoms like more light and will grow in areas of the sand bed with full light and on the glass. Their appearance is more "peppery" rather then forming a solid mat like cyano.

Hope that helps.

[Mr_Cool]

Yea, that's great. Am I over feeding then? I try not to let the food sink to the bottom. That is, I only feed what the fish can eat before I give them more. I'll try adjusting my power heads to get more flow in these areas. Thanks Gary!

[GaryP]

You are not necessarily over feeding. Alot of stuff besides food can contribute to detritus. Some detritivores to clean it up would be helpful. Hermits, nassarius, brittle stars, bristle worms, and some tangs are good for that sort of thing.