pH Monitor and Controller

[stuckpipe]

I am having a new inground pool installed and I am wondering if it is worth have an automatic pH monitor like a Polaris WaterMatic C2100 ORP/pH WaterMatic Controller installed to take care of monitoring and controlling pH?

Would it optimize my chemical usage any better?

Any thoughts?

[PoolDoc]

I'm going to sort of exercise executive authority here: the OFFICIAL Pool Forum answer to the question, "Are pH / ORP controllers a good idea for home pools?" is almost always a firm "No!".

There are several reasons for pulling rank on this one, besides the fact that I can since it's my forum.

First, I'm probably the only person on the forum with extensive experience operating pools with pH / ORP controllers.

Second, I may be the only person besides Chem Geek who is even aware of the problems that exist when ORP is used to estimate chlorine levels, when a pool is stabilized.

Third, I'm among the very few people here who have some idea about just how random the output of pH meters can be, if they are not calibrated.

Fourth, I'm also probably among a very few people here who have extensive experience with a full range of chemical feeder systems, which are an essential element of a pH/ORP control system . . . unless you are planning to have it ring a bell in the house, when it wants YOU to run out and add chemicals.

And, until someone understands all those things, they aren't really ready to recommend pH / ORP controllers to anyone. If anyone would like to tackle this question technically, please start a thread in the China Shop, and post here indicating that you did so.



So, why NO pH/ORP controllers for home pools?

1. ORP is its own thing (redox potential) and has a rather uncertain relationship to chlorine levels. ORP and chlorine levels ARE connected, but NOT in any reliable way on outdoor pools with stabilizer. As a result, it's VERY hard to get stable control with such a controller. Several controller companies, notably including the industry pioneer, Stranco, have attempted to argue (rather dishonestly) that stabilizer was a bad thing in pools, when the real story was that it was bad for their controllers, not for pools.

2. Using wetted electrodes to measure chemistry is intrinsically unstable. A pH meter that was EXTREMELY accurate last week, may be extremely inaccurate this week. This does not mean it's broken, just that it needs to be calibrated. Some expensive systems are more stable, but it's very unlikely that any pool control units incorporate these.

3. pH/ORP controllers don't do ANYTHING themselves, except turn one (ORP only) or two (pH & ORP) switches on and off. For the controller to work, you have to have some sort of electrically driven feed system for chlorine and for pH control. Also, all pool pH controllers are unidirectional (they can feed either acid or base, but not both) even though pH can go both ways.

4. Few homeowners, and virtually no residential service guys or builders, are prepared to properly install, much less maintain, an acid feed system. The advent of reliable SWCG (Salt Water Chlorine Generators) in the last 10 years, has given homeowners a reliable, electrically controllable, chlorine feed system, BUT . . .

5. Adding a timer to an SWCG can provide better control on outdoor pools than an ORP control unit . . . IF you know what you are doing. And, if you don't, neither will work well.



In short, pH/ORP control systems for home pools are just a marketing gimmick that allows companies to sell high end, "high tech" and HIGHLY PROFITABLE gizmos.


If you want simplified reliable feed, make sure your pool is 'salt-ready'*, and have a good, somewhat oversized, SWCG installed.

PoolDoc


"salt-ready" could mean a number of things, but does mean at least two: make sure your builder uses BRONZE ladder and rail anchors, NOT zinc. And, make sure your heater (if any) has a cupro-nickel or other salt-ready heat exchanger.

[chem geek]

I'm not fond of ORP and see it, at best, as a process control system for chlorine that requires manual setpoint setting and can be flaky. As for ORP correlation with active chlorine levels in real pools, there are graphs showing this in this post.

[PoolDoc]

Very interesting graph, Richard.

Uh, maybe I should say, very interesting graph to me . . . and maybe 4 other people in the universe ! I've got questions, but they are China Shop questions, so I'll hold off.

Ben
"PoolDoc"