Ask 'Dr. Spa' Q & A Message Board

: My question still remains... Is there a need to change the water and
: mineral purifier more often (i.e. quarterly) in order to avoid some
: type of damage to the equipment, or will changing the water in cycles
: dictated by water quality be sufficient. I am now heading for the 5th
: month with very clear and stable water and I am looking to do the
: right thing without unnecessary expense or effort.

I am with you on managing water with whatever tools are necessary. As far as risks with leaving the same water in the tub for an extended period: Obviously as you add stuff to the water, the total dissolved solids build up, and some people claim that you actually reach a point of saturation, where chemicals are less effective. If you are using dichlor, CYA also reaches levels that are above recommended guidelines. I know it is time to change in two ways, the water clouds or fizzes up when the jets are on, and it takes longer to clear after the jets shut off. Near the end, I also notice that I need larger doses of sanitizer to maintain clear water, perhaps due to the CYA. With regular use, that time comes in 3-4 months for me, during the summer when use is light, 5-6.

Other than those issues, I see no need to change the water for change's sake, and could make an argument that there are reasons not to change the water anymore often than necessary. First, you have to rebalance the water. It is theoretically possible that you could cause damage to the tub in the period between fill and achieving balance. Second, if you are using a mineral cartridge, you are probably dumping out perfectly good silver and copper ions. I know that N2 recommends replacing their unit every 4 months, but I have the impression this is due to an expectation that water is changed 3-4 times per year, and the metals need to be replenished after a change. Third is the cost of the water and reheating the tub, along with the environmental costs associated with water, sewage, and electricity.

That said, I also have seen posts by respected voices who are of the opinion that fresh water is a cheap way to clean up previous problems, and one person who feels that fresh water is a luxury he likes to indulge every two months, somewhat along the lines of your desire to adhere to a rigid schedule, and change before any deterioration shows up. Most people seem to think that a regular 3-4 month schedule is a good compromise.