You are correct, Equilibrium contains a lot of potassium. It contains more sulfate than anything else, as the calcium, magnesium, potassium, iron, and manganese it contains are all sulfate compounds.
It's generally thought that extra potassium or sulfate doesn't hurt anything, but I often wonder where one should draw the line... if 100 ppm potassium OK? How about 200? 300? 1000?
The general European and Asian school of thought is lower total dissolved solids (TDS) in the water column. I wanted to lower my water's TDS and eliminate extra chloride and sulfate while remineralizing my RO water.
I dose Flourish, Fresh Trace, Flourish Trace, Excel, Potassium, and Iron throughout the week (as per label).
After lots of testing and experience, I only reconstitute my RO water based on what needs to be added from last week's test results. I use:
- Calcium Carbonate
- Potassium Bicarbonate
- Ferric Nitrate
- Manganese Carbonate
My targets are 6 dGH and 5 dKH. I use a gram scale to weigh it. I adjust the measurements based on the previous week's test results.
I don't need to add magnesium because more than enough (more than I would like actually) is added through the Seachem products. (There have been some threads recently on various forums that magnesium levels greater than 10 ppm (41.18 ppm as CaCO3) cause problems with certain plants (for example, it stops rotalla wallichii from growing completely).)
I use a magnetic stirrer to stir the calcium carbonate for 1 hour before adding to the tank. I only add it when the CO2 is on, as the CO2 causes it to form calcium bicarbonate which is a soluble state. It takes about 1-2 hours to dissolve clear.
I don't test for iron or manganese; on a water change I always add the same amount, which is only a trace amount: .04 grams of Fe(NO3)3•9H2O, and .02 grams MnCO3. (I have a 42 gallon tank and change 15-16 gallons of water per week.)
I get my chemicals from a lab supplier.