I am not familiar with Hydrostone, but there is a product "Hygrostone" available from Jesse at growinhydro.com.
Yes, PrimeAgra is good, it is optimized for hydroponic growing, rather than being a remarketed concrete additive.
However, neither product can be shipped to Europe with even the slightest hint of an economical shipping cost, so I suggest you look for EU-sourced material.
Do you have any hydroponic suppliers there in Sweden?
Here in the states, any hydroponic supplier will have Hydroton or something similar to it. Best places to check out for what you need.
Any hydroponics store or growshop should have some sort of Leca (hydroton or other), and I see some in large garden centers that have a hydroponics section. The stuff is crazy heavy to ship, so if you don't want to pay a fortune in shipping, it's best to hunt around where you live.
__________________ Camille
Completely orchid obsessed and loving every minute of it....
Ok I'll look for a supplement for your product then Ray. Ordinary LECA dosn't seem to work as well thow. Pity that you don't have a distributor in Europe. Something to consider maybe?
Johan