i honestly think thats a myth skene any cyno i have seen grow has been in high and low flow. for me its in high flow. i have very high flow in my tank (sps dominated). the problem with the cyno i have is it grows only on the sand i have very little algae on the rock. so in order for me to take the cyno out i have to scoop my sand bed out of the tank which is fine but then i eventually have to re add new sand to the tank. i have amazing tank husbandry and i have never been able to avoid this stuff it blows my mind. 15 gallon water changes every week, 0 phosphates, 0 nitrates, feeding every other day, their are only 4 fish in my tank, good protein skimming (swc 150 bmk), Only use RO water. so i am at a loss.