Justin,As far as under aerated when you say 6 plate system are you using 6 plates of 4 stones such as ALA4GL or the 6 per plate ALA6GL ? If 4 stone plates are being used (and Im going to make some general assumptions so correct me where needed)you may be under aerated, If you have 20 available CFM and 3.33 cfm per station you may want to add some additional diffusers. I believe the operating range for the 4 plate is somewhere around 2.4 cfm max.which means you could add 2-3 additional plates if you stay with that model.This is also assuming the pumps are 10 psi models and not 15 psi models which provide less cfm's.Your total lift which is probably in the 1.3- 1.6 turns per 24 hours may be fine but all of the gallons probably arent being effected since you have shallow water.Im using diffusers in 6 ft minimum depth of water .Also if these are square stones turn them on "edge" on the plate to expose more of the total surface area vs the way I usually see them mounted flat with only 75% (3 sides) exposed.Is Hydrothol 191 out of the question for the goals listed ??I also thought Michigan had gone to a zero "P" in the lawn care industry.