I changed everything up last weekend to try and help but so far no luck. I have a 9.5 return and two K3's in the tank. I feel I have a lot of open space. I also turned off my MH for 2 days and it helped. I turned them on for a day and it got worst. So right now they are off for the weekend. I do have some VHO sups running for 10 hours. My MH run for 6 when I have them on. I use my turkey baster to blow it off the rocks and the sand bed, then I do a water change and try to syphon as much as I can out. I'm trying to be proactive about it as much as I can.