Wow! That certainly is soft. 
Personally, I'd say keep an eye on your CH over time. Unless you're exchanging a lot of water, even that 10ppm will build up over time. The key is watching the CSI measurement in PoolMath - keeping that as close to 0 as you can should work, and you can do that just fine with a 270CH.
Personally, I'd say keep an eye on your CH over time. Unless you're exchanging a lot of water, even that 10ppm will build up over time. The key is watching the CSI measurement in PoolMath - keeping that as close to 0 as you can should work, and you can do that just fine with a 270CH.