I need to know what size plant/soil you are trying to feed. The general answer is... not much at all. I add about a tablespoon per plant at feeding time... in 3 gallon pots. This dose lasts about a week to two weeks, depending on conditions in the grow room. It really comes down to knowing --by looking at the plants-- how much guano is needed. Just be conservative with your doses at first, and increase until you find the sweet spot.