Making Fertilizer yourself? Any Recommendations

I did read that some people buy fertilizer from JRPeters and save a lot of money.
Can you recommend me some fertilizer for hydroponics (rockwool) so I can save money?
I am based in europe.

At the moment I use General Hydroponics Flora series.
I already plan to make CalMag myself as I am using Reverse Osmosis water.

this thread talks about cost-effective dry salt fertilizers
https://www.rollitup.org/t/chem-gro-vs-jacks-vs-mega-crop.974125/
if you're ridiculous enough you can try my 10 part formula