There have been many questions regarding the use of salt and these are always followed with allsorts of do's and don'ts so here is a basic FAQ on what salt you can use and what the risks and dangers are.
Using iodised salt.
The iodine in the salt is in the iodised salt of iodine (this usage of salt is in the chemistry format, i.e chemical symbol for Iodine is "I" and iodine, sodium iodide is the sodium salt of iodine and is written "NaI"). The long and short of it is that any of the iodine salts used in making iodised table salt are inert and cannot react in water. Not using iodised salt is just another fishkeeping myth.
Using salt with anti-caking agents
The most common anti caking agent used in salt is YPS (Yellow Prussiate of Soda or more correctly sodium ferrocyanide). The theory is that this will break down and release cyanide and poison the fish. The conditions required to break down sodium ferrocyanide are extremely unlikely to be found in an aquarium, let alone a discus tank. It requires massive amounts of energy, it is possible for the sun at midday at or near to the equator to maybe break sodium ferrocyanide down, but last time I looked very few of us have the sun as a tank light. If we were to put sodium ferrocyanide into a strong acid then it would break down and produce cyanide gas (HCN). So, how many discus or fish have we got living in a strong acid? And finally, given that the maximum permitted amount of sodium ferrocyanide in the EU is 20mg/kg that is 0.00002% and will no doubt be a similar tiny amount in the USA you would need an awful lot of salt to have any effect! Yet another fishkeeping myth.
The moral of the story
Use any salt you want to, the cheapest you can find, I have been using whatever salt I can get hold of for all my fishkeeping life and have yet to poison myself or the fish with cyanide!
Regular use of salt
If you want to always add salt to a discus tank, stop, sell the discus and buy some mollies or even go the whole hog and get a reef tank!
