Partial drain due to CH


LifeTime Supporter
Jul 28, 2007

I'm 18 months in to my new pool and have watched the CH rise from just over 400 (14 months ago) up to today's high of 620.
I believe it's time to partially drain and refill. That being the case I have three questions which I could do with a few pointers on:

:?: My CH is 620 now and my fill water has a CH of 120. Do I just go for an easy "half the pool" and hope that I end up around CH 365 after refilling or do I need to be more ambitious?

:?: What do people do for pumps? Is there any way I can use my pool equipment to pump this out? I could go and buy a cheapo sump pump from Lowes for about $80 or go and rent a trash pump from Home Depot for the day for about $50?

:?: What causes my CH to rise? Is it a CSI of <-0.3 pulling Calcium from the plaster or a CSI of >0.3 about to dump it all over my plaster? I think I am completely misunderstanding the whole CH thing but please take the question in the ignorant spirit in which it was intended! :oops:

Thanks for your support TFP team (as ever!)

Numbers d'jour:
pH 7.6
FC 6.5
CC 0.0
TA 80
CH 620
CYA 50
Borates 40(ish, it's between 30 & 50 on the test strip)
Salt 3900
Temp 82
CSI 0.08


LifeTime Supporter
Jul 28, 2007
Good point - should have mentioned that I'm a full BBB convertee!
Bleach, Borax, Baking Soda, CYA & Muriatic Acid are the only things I've used for the last 14 months. :-D


LifeTime Supporter
Platinum Supporter
TFP Expert
May 7, 2007
Silver Spring, MD
As water evaporates the calcium stays behind. When you top off the pool more calcium is added, so over time the total amount of calcium goes up. It is possible for calcium to come out of the plaster or deposit as scale but both of those require fairly extreme values of the saturation index and really won't happen if you have been keeping your PH under control.

In arid areas with high evaporation rates and high CH fill water it becomes impractical to keep CH levels down near the normally recommended levels. With careful management it is possible to allow CH levels as high as 1,200 to reduce the frequency with which you need to replace water.

It is possible to drain the pool with the main pump, particularly if you have a main drain. With a main drain you just block the skimmer and the pump will pump the pool down. The one issue is that once the pump stops you will be unlikely to be able to prime it again until you have raised the water level back up. Without a main drain you will want to use a vacuum hose to draw water from below the skimmer. When using a vacuum hose there is some tendency to lose prime, this can be minimized by using a small pump to pump water into the skimmer, covering any leaks with water.


LifeTime Supporter
May 4, 2007
Did you notice dust while brushing? I also had CH rising after new plaster install. I have Diamond Brite and I suspect the installers did not acid wash. I did not see the aggregate until months of brushing. My fill water has 110 CH and in 12 monhs it went up to 540. I saw a lot of dust on my floors and walls when brushing. My calcium held at 540 for about a month and I drained half the pool. I cleaned the cartridges as well. Now my pool is holding at 350 and I do not notice any more dust. Also my PH has not been rising as fast in the last 4 months.