How Long to See the Effects of a Deep Sandbed?

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I ask because I had a pretty good outbreak of hair algae and brown diatoms. I also have been adding live sand and dead sand to raise the level to about four inches. It's been about two weeks since I have reached that four inch level and now there is no sign of brown algae and the hair algae is almost completely gone.
The tank is about ten months old and is a 75g. I also only add tap water(no RO/DI yet).
Is this the benefits of the sanded or is something else at work here? Is it just the tank going through it's natural progression? Either way I'm pretty happy about it!
I'll give you one mans wild guess.

If you get the sand deep enough, and bacteria were present before. at least some of them can use oxygen and break down
things or use NO3 when oxygen isn't available. So you may have some ready made anaerobic bacteria with a taste for nitrates.
However, in a new tank, there is an algae "progression", with different types blooming and receding. Sounds like that could be
happening at the same time.

Hope this helps;


You will know when your sand bed is working effectively in denitrification by the appearance of bubbles (gaseous nitrogen) within the sand bed. These may start off small, but can combine to form pretty large pockets of gas within the bed trying to make it to the surface of the bed so that they can rise and exit the aquarium. If you do not have a plenum in the tank, you may also start to see zones of anoxic denitrification within the sand as appearance of black areas of hydrogen sulfide pockets. If you do not disturb these areas (and you shouldn't) they will resolve. These are two indicators of a functioning deep sand bed (at least for denitrification). A third would of course be a drop in nitrate levels in the tank.
The disappearance of algaes may also be due to the aging of your tank. But the sand bed if properly maintained will go far to controlling these problems. A switch to RO/Di water and good skimming will also help.

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