No need to drain due to high CYA

markl67

In The Industry
Jan 1, 2013
9

CYA at 120-140 is not a problem. Please dont drain because of that alone. I own a pool service business and I know from experience that what is typically considered high CYA really isnt. Free chlorine's ability to kill bacteria and algae isnt impacted at these levels. Thats been proven.
 

PAGirl

TFP Guide
Jun 5, 2012
2,389
Central PA
Re: I will be draining to deal with high CYA, but...

CYA at 120-140 is not a problem. Please dont drain because of that alone. I own a pool service business and I know from experience that what is typically considered high CYA really isnt. Free chlorine's ability to kill bacteria and algae isnt impacted at these levels. Thats been proven.

That's not the method recommended here. It causes the need to keep a higher FC level. If a problem arises, the levels needed to battle the algae make it difficult.

Here are the recommended levels:

Pool School - Chlorine / CYA Chart
 

JoyfulNoise

TFP Expert
Platinum Supporter
May 23, 2015
15,884
Tucson, AZ

CYA at 120-140 is not a problem. Please dont drain because of that alone. I own a pool service business and I know from experience that what is typically considered high CYA really isnt. Free chlorine's ability to kill bacteria and algae isnt impacted at these levels. Thats been proven.
Your wording is deceptive - yes, FC is not affected by CYA because FC includes all forms of free chlorine (hychlorous acid, hypochlorite ion and chlorine bound to CYA). What is affected by CYA is the active chlorine level (hypochlorous acid concentration, or [HOCl]). In order to kill pathogens and algae, the FC level needs to be at least 7.5% of the CYA level in order to provide enough HOCl to have reasonable CT kill times. This has been proven extensively in peer reviewed, scientific literature and has been detailed extensively on this site, particularly in the following threads -

Pool Water Chemistry

Certified Pool Operator (CPO) training -- What is not taught

You claim to own a pool service company. Your experience is based on a model of pool care that we do not advocate. Because we advocate self-testing and reliance on minimal, daily pool care (testing and dosing the water as needed), our members can operate their pools at lower CYA and FC levels. Because your service and profit model only allows you to visit a pool once per week, with service times less than 30mins per pool, you must use higher doses of chlorine and CYA in order to keep enough chlorine in the water to be effective in between service visits. Excessively high CYA can be used to manage and maintain very high FC levels and is often found in service companies that use chlorine gas injection (CYA over 100ppm and FC levels above 15ppm). These companies are following, in many respects, the FC/CYA ratio advocated here, they just do it at higher levels.

This technique of using high CYA in combination with high FC will not work for the average pool owner as they do not have access to chlorine gas systems which add no additional byproducts to the water (eg, salt from liquid chlorine or calcium from cal-hypo). A typical pool owner, operating a pool with a CYA of 120ppm, would require several gallons of bleach per week to keep the pool water at a proper FC level and thus would be introducing a lot of excess salt into their pools from all of that bleach use. The situation would worse if they used cal-hypo powder for chlorinating. If an algae bloom does form, the required amount of bleach to raise the FC to shock levels would be incredibly expensive.

So unless you can provide evidence and data that shows that pools can be run better using high CYA levels, TFP will keep advocating for the lower levels of CYA as evidenced by the tens of thousands of pool owners on this site who have clean, clear and healthy pools. You are welcome to use whatever methods work for your business model, profit margins and customers but please do not post statements on this forum that go against what we teach here unless you can backup your assertions with peer-reviewed evidence. The foundational principles upon which TFP rest are solidly based in science and fact and the methods we teach are based on those scientific principles. While your limited experience may work in certain situations, it is not broadly applicable. The TFPC Method of pool care has been shown to work broadly across many different pool types and climates.