the problem w/ letting it run its course if for those of us that dont/cant use RO water. Like in my case my ATO adds new water bout 3 times daily so more diatoms are added 3x daily so it is just a continuous thing to deal with but so far the phosgaurd is working well. However I do agree with Europhyllia in that if you can do us RODI water as it will make a huge difference. I used to use RODI when my tank was in SA and never had any diatom issues now that im on tap water I dont think i have had a day w/o any but now that i added the conch and the phosgaurd it has gotten substantially better and is getting better daily