i have a 75 gallon tank. on the backwall alittle left and alittle right of the center I have two powersweep powerheads (270 gph). the one does not sweep anymore and the other sweeps very slow and basically is all clogged up with coraline growth so it doesnt sweep to much. on the right side of the tank I have a maxi jet 900 (230 gph). on the backwall down towards the bottom shooting behind the rocks I have a maxi jet 600 (160 gph). the far left upper corner I have my sump return. at night everything is runnying ect the one powersweep. I am looking to upgrade my powerheads what are good ones and what ideas on placement are out there to combat my "dead spots"? also what do you mean by alternating? like a wavemaker?