Pool Water Change by Newbie!!How much % to change and why??


Jan 13, 2008
Pool Water Change!! How much % to change and why??

My Pool water hasn;t been changed in over 8+ years and have noticed its hard to keep up with chemical demand.

I have to ad over 200% acid of what i normally have been and less chlorine to keep the Ph level in sync.

I'm installing a new Intelliflo Pump and Quad 60 DE filter as my equipment is from 1972 and very ineficient.

1....How much pool water do i drain and refill?

2...Is there a test i can do to tell what percentage to drain?

3...Why do we have to drain our pools?

4...Do i have to be concerned about "Pool Popout" in my So. California area? We have had some rainfall lately.

I would like to put in an inline chlorinator but my funds are depleted because of Pentair equipment purchase. Is there an ecomomical way to put in chemicals better than by hand until i have the funds to go to automated salt water system?

Thanks .........Gman


Mod Squad
TFP Expert
Apr 4, 2007
SW Indiana
gman66 said:
3...Why do we have to drain our pools?
You don't have to routinely, but if you are using pool store chemicals you may have high CYA, high calcium or both. Get a good test kit and analyze your water to find out what you need to do. A member here sells a good one at tftestkits.com, or you can buy a Taylor K2006. Any lesser test kit doesn't give you enough information to maintain a pool well.

I would advise against regular use of an inline chlorinator. Trichlor adds CYA rapidly to the water which can lead to overstabilized water. Most of use that don't have saltwater systems use liquid bleach poured in by hand, and only use our chlorinators when we are on vacation.


TFP Expert
Platinum Supporter
LifeTime Supporter
May 7, 2007
Silver Spring, MD
CYA is cyanuric acid, often called stabilizer. The higher your CYA level the more FC you need to keep the algae away. Trichlor, the chlorine source used with tablet feeders, is "stabilized" with cyanuric acid. The more trichlor you use the higher the CYA level, the more you need to use and eventually you can't keep up and get algae.

There is no need to change the pool water unless there is some specific problem. Get a full set of test numbers (at least FC, PH, TA, CH, and CYA) and we can tell you what you need to do. By far the best idea is to get a good test kit, such as the TF Test Kit, see the link in my signature, or the Taylor K2006. But if you are in a hurry you can start with test results from a pool store.