Black algea in the betta tank

[freefour]

I was doing my weekly pwc and was vacuuming the betta tank . Turned up some of the gravel and a black goop got sucked up , and smelled terrible , stunk the den up really bad. Well I got done and a lot of the gravel in the middle of the tank is black stained now. I was going to change out the substate to sand but now I'm kinda worried about this stuff. I had read something about this some ware in here or on the web but for the live of me I can't find any pictures to confirm. What I had noticed is that it was like a black slime and it was under the gravel. Not hairy , from what I could tell and it's not on any thing above the substrate. I also had a problem with diatoms but they have subsided a lot and I didn't pull much if any this time. Any suggestions?

[Devilishturtles]

Sounds like a case of cyanobacteria, which can appear black or dark brown in anoxic (low oxygen) conditions, like under the gravel. Unfortanetly, this algae isn't very easy to get rid of. So, that said...

What kind of lighting do you have, and how many hours a day is it on?
You say you do weekly water changes. Does that include vaccuming the gravel?
What size is the tank and are there any fish besides the betta?
Do you have just regular aquarium gravel?
How often do you feed and how much. Does it all get eaten or does it fall to the bottom?
Can you test your water and give us the readings? (ammonia, nitrite, and nitrate)
Do you know if your tap water contains phosphates?

Lots of questions, I know.

HTH

[freefour]

Well the peramiters are all ok , nitrates, amonia , and nitrite are all normal, The gravel is noncolored river gravel (brown gravel bought at Wal Mart) ,Feed him about 5-7 pelets twice a day and he eats all of them (hand fed) don't know if the tap comtains phosphates or not. Yes I vacume the gravel every pwc. 5 Gallone hex tank. Only an apple snail with him. The light I have on them is a desk lamp ( 40 watt bulb ) held over the tank with a white ceramic plate for the lid. The light shines threw the lid lighting the tank up but it is a low light , he kept seeing himself in the glass that is why I put the plate over the top ( well for that and I didn't have a lid). The tank has had problems with diatoms befor right from the start. It was given to me and it was filthy and stored in a damp basement with the old gravel and everything else inside for several years . I threw everything away and cleaned the tank befor I cycled it and everything . Think I am just going to need to get a new tank and start from scratch?

[severum mama]

Try cutting down on your feeding, maybe that will help with the amount of nutrients in the water. On the package of my betta pellets, it says to feed 2-3 at a time.

[freefour]

I feed him twice a day.

[Devilishturtles]

Likely a combination of everything. Cyanobacteria feeds off of a tank with lots of DOC's in it. Reduce feedings and increase water changes.

Do you have a power filter on your tank?

If you want to switch to sand, follow the article in the articles page (link at the top of this page) to do so w/o a cycle.

HTH

Also, did you have an ornament or object sitting on top of this area of the gravel? Compacting and hiding aeration from the gravel will cause anoxic conditions.