I use a mix of these
Masterblend 4-18-38
YaraLiva Calcinit 15.5-0-0 (Greenhouse Grade)
Magnesium Sulfate(epsome salt)
we mix it 2 to 2 to 1 in a gallon jug of water to put in my hydro setup.
I get it off ebay
https://www.ebay.com/itm/2-5-lbs-Mas...item2a7cef73b2
Works great so far.
I change it out every week or two and dump the old on our potted plants.
I use it in our down spout set up