That part is up to you to figure out by genetics. Some strains need more and some don't. Some take more nutes up and some don't. If a strain is a heavy feeder, go with the 50, or if you are not sure use 25. You can alway's make 1/3 batches and go with different ratios of worm poo in each batch. Label them, then find out which works better for the strain you want to grow.