sand or gravel?

[Paulcm10]

I prefer the playsand for bottom dwellers. The PFS was not sharp but it was larger grain and it makes digging through the substrate harder, IMO.

I find with playsand my geos can sift through the sand easily and pass the sand out their gills. With PFS I don't think that they would be sifting through the sand. The grains are too large to pass through their gills.

Another note, I've never had a diatoms bloom when using playsand. I had a terrible bloom when using the PFS that lasted for months.

i have heard about the diatom bloom.
can you explain that to me cause I do not know what that is?
i read that you get diatom bloom if the grain size is big?