My experience with potassium was highlighted during an aquaculture project using filtered natural seawater that was low in potassium. I was advised by Steve Garrett, the outdoor coral system trailblazer in California, to make sure to correct this potassium deficiency. He noted that when tested his system was running at higher levels of potassium and doing great. He keeps a wide range of very colorful SPS, and flocks of Xenia growing in his outdoor glass aquarium of wonders. He has noted long term consistent growth with his Xenia with no crashing. Steve lends that to the potassium.
Potassium is part of my regular reef husbandry regime. I have been using potassium chloride for years and doing so I have had much brighter and more intense colors. I have also had faster growth on my soft coral and macroalgae. I think it’s probable that the potassium in the Lugol’s what grows the Xenia. Perhaps the iodine alone is not as critical as potassium. I do very sparse iodine dosing, and all is well as far as growth and a lack of colony collapse are concerned. I do however dose iodine to enhance macroalgae growth when needed.
I’ve noticed potassium enhances certain pigments especially pink. I had color enhancement effects within several days of dosing. Iron dosing (which I will cover more in he future) helps develop brown pigments, healthy background color, and deep toned greens. This in part seems due to enhanced zooxanthellae growth. Potassium has a more striking effect on the coral’s fluorescent proteins. Pinks, Purples and Reds respond most profoundly. Pink and Purple Pocillopora and Stylophora start emanating eye blasting hues. Neon Green and Orange fluorescence are all kicked into overdrive as well. I use the hot pink Stylos as a visual litmus test. It stays super bright pink with daily dosing. With slight overdosing the pink gets crazy bright and bleaches a little. Low potassium and the colors are dull, even brown.
Potassium, because it is a nutrient, will cause increased nuisance algae growth in the presence of elevated nitrates and/or phosphates. Potassium will support the photosynthesis of all photosynthetic species, including macro and micro algae. This works great in a refugium, as the macroalgae grows quite lush. However a hair algae forest in your tank can wreak havoc on your husbandry routine. Make sure your phosphate and nitrate are not highly elevated before you dose.