So, I was at our club's Spring Fest a few weekends ago and I had a great discussion with one of the speakers afterwards (Justin Credabel) regarding the role of Potassium in the reef aquarium. His presentation was mainly related to Goniopora species and I didn't get a chance to hear all of it, but when I heard him talking about K my ears perked up so I grabbed him afterwards. Basically, he told me that it's pretty hard to OD on K. He has ran tanks at 900-1000ppm and seen no negative side effects (400 is NSW). He also mentioned that negative effects can start to show up when you get into the mid to low 300s. Scrubbers suck K down like a 10 year old sucks down a shake from McDs. Trying to keep K and 400 in a scrubbed tank can be a challenge but I haven't worried too much about it as I really didn't see any negatives when running K at 350 or less even...but that doesn't mean I should be running it there. I use the Salifert Potassium (K) test kit. Very easy, fairly accurate. I've heard that the kits in general are good for noting differences from one test to another, but that the accuracy of the reading itself might not be the greatest. What that means is if you test one time and get 400, and the next you get 370, you can be sure that your K dropped 30ppm but your readings of 400 and 370 might be off (but equally off). So you might have 410 and 380, or 390 and 360. End of lesson. Now, as for K dosing, he runs a constant drip. Now that makes me say "dang bro you must have extra cash laying around" because even buying Brightwell Potassion-P, which is powdered concentrated K, is expensive considering the amount you have to dose just to maintain 400ppm. He told me however that he uses Morton Potassium Chloride in bulk bags. The downside is that it has Phophates, not a ton, but some. He mixes it up in a bucket, and says that the chloride offgasses so you aren't throwing off the ionic balance by dosing it. Not sure it all offgasses, but that's irrelevant as you will shortly see. Then he drips it into the tank through GFO and this takes out the phosphates. I thought, dang, that's awesome. Next, he says that he also drips Iron Sulfide. So I'm thinking, Iron Sulfide + Potassium Chloride, no problems with ionic balance, and you get K and Fe, both good for tanks, corals, scrubbers, etc. Win Win Win. I'm not sure on the source for Fe but I'm going to find out. Iron is highly reactive in the reef tank and get depleted out nearly immediately. It's hard to OD Iron. He explained the mechanism to me and it's gone, it's been a week or so and I've forgotten most of the discussion but there is a mechanism as work that reduces Phosphate out of the water column very quickly when dosing Fe and I believe K also. The point here is though that when using an algae scrubber in a high K environment, the excess K will cause algae growth to pull N and P out of the water column faster. The result? Supercharged Algae Scrubber. Possible reduction in the "clean-up" time in a dirty tank. Possible method of fueling an algae scrubber in order to out-compete tank algae (think dripping Fe and K at the scrubber input). Possible method of faster reduction in water column nutrients in a neglected tank. Possible solution to N=0 but P still present in water column. So this is kind of a big breakthrough that I still need to research and gather info on, but I wanted to start this thread and open this up to the tech heads and chemical geeks who have more time than I do. I'll be in touch with Justin for some more clarification as well. DISCUSS!