A lot of times hobbyists use products and dont see any serious harm so they assume its doing its job properly. their corals live so they think its due to the product. more often than not the plankton is doing little except possibly feeding the natural scavenger and micro fauna in the tank boosting population levels. wich in turn feeds the coral BUT if you use appropriatly sized live planktons you can feed your corals and the microfauna instead of just getting a secondary effect of a higher microfauna population.