Why recommend or not recommend stirring sand?

[Mark Shelly]

In some recent posts, some people have recommended not stirring up the sand bed when covered by diatoms, dinos, or even cyanobacteria. Why?
I understand that if you have an old sand bed you might release hydrogen sulfide by stirring. But wouldn't stirring the sand bed before water changes be good if you do it all along? I had what I thought was cyanobacteria on my rocks and sand. I was following the hydrogen peroxide thread and even got some to try when the final report came out. But I had also modified my flow over my rocks, stirred the sand, and turkey basted the rocks (before I read not to from twillard), and into the sand for several days. The mats showed up in a few new spots and I hit those as well. The cyanobacteria then started becoming less apparent. Now it is almost gone. I suspect that it was more that they were removed from the system when stirred by my HOB protein skimmer and/or trickle filter pads (I don't have a sump).
My thinking with the sand bed is that if you oxygenate and stir the sand bed as you go, it shouldn't get toxic. I have a cheep test kit, but my phosphates and nitrates are always low, with coralline algae growing well. So, is there something I was missing that others have discovered over time?

 

[Diesel]

By stirring you move it only as you not attacking the problem.
In your case I think it might be spirulina that by regular maintenance will disappear.

 

[Mark Shelly]

By stirring you move it only as you not attacking the problem.
In your case I think it might be spirulina that by regular maintenance will disappear.

I was wondering if this was the case. I only have 40x on my microscope. The matt appeared to consist of straight fibers, I just could not verify if they had many cells or the straight fibers were spiral wound. I also saw a few larger cells that appeared to be protists of some type with distinct organelles.

 

[Diesel]

There's a method to find out if this is Cyano or spirulina tho.
Lets see if @twilliard can help you out on this.

 

[TaylorPilot]

My school of thought has always been that you can stir thin sand beds of an inch or so because they are too thin to create an oxygen free layer, but you shouldn't disturb deep sand beds because you can release allot of nasty stuff, and introducing oxygen can kill off stuff that is living in that anaerobic layer. JMHO

 

[twilliard]

Yes there is a way to determine between cyanobacteria and spirulina
https://www.reef2reef.com/threads/positive-identification-of-cyanobacteria.253287/

Now the reason I say not to stir the bed is when doing the treatment you stand a high chance of spreading the issue.
Now as the treatment progresses then it can be easily siphoned (not stirring) to pick up the problem area so the substrate underneath doesn't become so anaerobic that hydrogen sulfide becomes an issue.