IIRC, the pool filter sand is silica sand. I am not absolutely sure, but it's worth checking out pool supply company. It may come in few sizes - pls. let us know what you find out...

I can't find the horticultural sand here in the U.S. That's been the most difficult one to source.

I have: pumice, coarse perlite, fine perlite, chicken-grit, turface, vermiculate, and seed starting soil. Out of all of that stuff, what should I use? I was just going to use the mix that is on the gerhard marx site. I assumed he would know what's up :)

Rina, the pool filter sand that I've come across seems too fine.

Mayo, .5cm = 5mm? That seems kinda big for sand. I am having enough trouble locating 1mm-2mm stuff.

i just use pumice.

Do you use a top layer of fines or anything like that?

It doesn't matter what you use..as long as drainage is good. Feed well diluted lower dose fertilizer with your waterings in the growth period. 10 52 10 a good one

Mayo, what size is your perlite? I have coarse/hydro, and the finer/common stuff. Would obviously have to sift the finer stuff. Which would be better?

10-52-10? That is a lot of unnecessary P. A 30-10-30 at 25-50ppm N works just fine and won't leach a ton of P.

I put a little fines on top of the coarser stuff.

Would foliage pro 9-3-6 be alright?

I use the sand in my photo above. It is not very chunky and the particles are small. It is something I would never consider planting anything else in. The amount of sand I pour in is to make a layer of around 0.5cm thick. So the seeds don't fall into the perlite and get a bit more moisture than perlite alone.

The sand comes in small bags, maybe 1kg. I bought it before I knew it wasn't good in soil mixes. Turns out I really like it for seedlings.

The perlite I use is medium-sized and from a local hydroponics store. I never measured the size. It's just a little bigger than what you find at big box stores (after removing fines). In the end, I usually just throw it out after. It's more to give enough surface area for the roots to grow against and keep enough moisture. Plus it's easy to remove when splitting the seedlings apart.

You could also try a thin layer of turface fines? Just not too much since Turface holds lots of water. If you put too many turface fines it becomes a soggy clump, which probably isn't ideal for seedlings.

foliage pro is fine

I use FP 9-3-6 and MG 12-4-8 with no issues.

10-52-10 fertilizer is one of those 'specialty' ferts; it will supposedly make blooms bigger and more of them (IIRC it is called 'Bloom booster' or something similar). Not suitable for succulents and as Nil pointed out, way too much P. I wouldn't use it for most of the plants - maybe for some annuals...