OK I have a 90 gal freshwater tank. 12 fish all cichlids with 3 plecos. I cant seem to find out on how often to add salt. There is no hydrometer to measure that low. Do you add salt when you water change? and what is the best way to add salt? I seen some tanks with a small container with salt added and a few holes on top for slow disolving. Or do you just add salt directly to the water. Any info would be great.