I also posted this in the chemistry forum.. but seeing as it’s a GHL O2 probe i thought it might be of interest to you all. I’ve had my GHL Oxygen probe for several weeks now and it’s been interesting to see how powerhead placement and overflow water height affect the levels, dropping the water level in my overflow by several inches really increased the O2 levels significantly but the noise drove me mad. Surface agitation seems to be the determining factor in my tank, I run 2 vortech power heads and these don’t seem to contribute a huge amount to my O2 levels if I run them 2/3rds of the way up in my tank as I like to. If I rise them in my tank O2 levels rise, I’ve found the best way for me to strike a happy balance is to have my Gyre pointing at the surface, I can keep my vortechs lower in the tank and my overflow silent, I have an Oxydator in the tank now which raised O2 levels by about 5%. Levels drop significantly overnight. I guess nothing surprising in the results but I wouldn’t like to be just running Vortechs alone in my tank at the depth I have them at now, but saying that is 102% sat O2 not high enough?