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Assuming you want to use a chlorine based system (for hot tubs, its called dichlor - AND NEVER TRICHLOR), take webini's advise and read about the "Vermonter method". Basically, once your water is initially balanced (pH, Alk, Calcuim), you only use two chemicals to maintain your tub. MPS (Monopersulfate, which is a non-chlorine oxidizer) after each use, and Dichlor (which is chlorine) to "shock" the tub once a week, or as needed.
Total chlorine (TC) is the difference between free chlorine (FC) and combined chlorine (CC) [TC=FC+CC].FC is the chlorine that has not been used yet. It has not sanitized or oxidized anything. It should be measured 20 minutes after adding and you shoot for at least 3 PPM. FC doesn not smell.CC is the used up chlorine. It has done it's job and is sitting there basically doing nothing. If it gets too high it will start to smell like chlorine. There are 2 ways to get rid of it - 1) get the FC reading to be 10x the CC reading & 2) which is the easiest IMO, use non chlorine shock (MPS) and have it do it's thing.A good test kit (Taylor k-2005) can differentiate between FC & TC, with the difference being CC. I used to use cheaper kits but found exactly what you found, they can't measure the difference in chlorine.Since you've gone a week and it is reading something, my belief is that you are measuring CC. Chlorine usually, unless you get chlorine lock, will disipate within a day or so.BTW, it is a good idea to shock the tub with chlorine every so often just so you kill anything that may have survived the 3 PPM routine.Hope this helps!
Hey Vinny...I think this is one of the best posts I've read in regards to chemicals! I'm trying to get this all figured out BEFORE our hot tub arrives in a couple of weeks so I know what the heck I'm doing. (And I'll also know if the dealer knows what he's talking about when they set me up!) When you explained the differences between FC, CC, & TC, a light bulb went off in my head....it actually makes sense now! Thanks for the time you give to this board to educate us "newbies". It is very much appreciated!--renee