I use Flourish. I know how sensitive the shrimp are that is why I do it outside of their tank. My shrimp tank is in the big bay window so on a sunny day I have to watch how warm it gets. I noticed the plants seemed not to be getting enough nourishment so I am trying this. I have mostly fast growing plants in there now and moss balls.
Don’t give up. I think everyone has gone through a dilemma in this department. Everything is trial and error, shrimp are really easy to maintain once everything is flowing. I have a 38L (11G) and a colony of blue/blacks, reds, yellows and ghost. I use the built in filter but have a sponge on the end of the input pipe and an air pump at the other end. I feed every 2nd day and add a fruit or veggie piece in for a treat once a week. I also have MS and MTS and ramhorn. When the MTS get out of hand I just cull as many as I want to keep the invasion at bay. They have a heater set at 22 degrees and I have the lights on for about 10hrs a day and open the curtains every other day to let some natural light in. I water change every couple weeks but keep an eye on the parameters in between. I really don’t do much at all, they are happy to be left in their little tank and fossick through the plants, moss etc
Start off with hardier beginner shrimp and go from there