must of missed this property CH

[JohnT]

See what your heater manufacturer recommends. That would probably be your guide.

[chem geek]

Though it is well known that keeping the water saturated with calcium carbonate is required for plaster/gunite/grout surfaces exposed to the water, it is unclear as to whether or not this is necessary to prevent metal corrosion, as in a gas-fired heater, especially using copper, or with stainless steel bars. There is also some growing controversy regarding increased corrosion in SWG pools, possibly due to the higher salinity, and it is unclear as to whether calcium carbonate saturation would help reduce such corrosion. One example of an indoor vinyl SWG pool not using CYA and having low CH and experiencing rather rapid corrosion may be found at this thread.

In short, I can't find a definitive answer to your question of whether you need to increase CH. It might be wise to increase the CH at least somewhat closer to saturation levels "just to play it safe".

In addition, you may find that with an indoor pool with no CYA that your swimsuits degrade faster (especially the rubber; plus some fading) as this is what my wife experiences over just one winter of swimming in an indoor pool compared to our outdoor pool in the summer where no problems are found with swimsuits. The higher effective chlorine concentration when no CYA is present *might* also contribute to corrosion, but that is pure speculation on my part. At any rate, one possible solution to these problems would be to use a small amount of CYA (10-20 ppm which you can't easily test for except to look for cloudy water where the black dot is still visible in the test) in an indoor pool since that will cut down the effective chlorine concentration closer to the normal levels found in an outdoor pool. This is *not* mainstream, so take this advice with justified skepticism. Also, it can be harder to control (i.e. keep low) combined chlorine (CC) levels in an indoor pool and using CYA and not having sunlight may require more chlorine to shock the pool, so it might be better (though more expensive) to use a weekly or bi-weekly maintenance dose of non-chlorine shock (potassium monopersulfate). Both the use of CYA and non-chlorine shock would lower (using CYA) or virtually eliminate (using non-chlorine shock) the creation of disinfection by-products (DBPs) which are a bigger problem in indoor pools partly due to the poor air circulation and lack of sunlight.

That's my two cents, for what it's worth.

Richard