Water Chemistry Questions

[dws3]

I recently resurfaced my pool with a Pebble-Tec mini pebble finish. Pebble-Tec recommends maintaining the following levels:
FC: 1.0-3.0
pH: 7.2-7.6
TA: 70-100
CH: 150-300
CYA: 20-30
CSI: -0.3-0.3

TBF/Poolmath have different recommendations. FC and CYA are fine, the differences are understandable based on the interaction of CYA with the efficiency of chlorine. But I don't really understand why the TBF/Poolmath recommendations are so different for other chemistry measurements. For example, TBF recommends an ideal range for pH of 7.6-7.8, which is above the Pebble-Tec recommended level. TBF has an ideal range for TA, 60-80, that has a low end below the Pebble-Tec recommended level. CH is way off the charts, with TBF recommending an ideal level of 350-550, far higher than Pebble-Tec's recommended level. TBF's take on CSI is understandable, since I think the concensus there is still to keep it in the -0.3-0.3 range when possible, but don't freak out if it goes as low as -0.6 or as high as 0.6 for relatively short periods of time. It is bothersome to me, however, that CSI is downplayed in a sense, emphasizing maintenance of the other parameters. It seems to me that CSI is the primary indicator of water chemistry balance, so as long as other parameters are maintained within measureable levels, CSI should be your holy grail.

So I guess I really have two questions:
1. Does Pebble-Tec have inside information on how their product needs to be maintained, or are they just blindly recommending levels that have been out there for decades?
2. When it comes to CSI, why wouldn't it be the primary parameter? Why worry about maintaining strict ranges on other parameters, as long as CSI is between -0.3 and +0.3?

Thanks in advance for your help in understanding water chemistry.

 

[onBalance]

You are correct and have the right understanding regarding why the CSI is the primary thing to keep water in balance.
PebbleTec does not have inside information. I think they are trying to prevent calcium scale, but they go overboard on their parameters. They seem far too low overall (CSI basis).
Keeping the CSI between -0.3 to +0.3 will serve your pool best.

 

[Texas Splash]

dws, for your concern, I think it's important we clarify a few things:
- If you are a plaster owner, CSI can be very important to you, but it is not as important to other pool types (FG or vinyl) unless it gets too high of course (scale).
- The emphasis of CSI over the other parameters falls on what's most important to that specific pool. For many, it's simply algae control, so CSI isn't as much of a priority.
- Believe me when I say we at TFP (MODS, Experts (like OB above), and many others) have debated the importance of CSI issue for a long time. In doing so, CH and other levels have been adjusted in an effort to ensure pool care is as user-friendly to the average pool owner as it can be without getting too complicated. It's a fine line I can tell you.
- The Recommended Levels page was revised a couple months ago for those reasons, expanding some ranges to allow pool owners of each type to see how wide a range they can safely maintain their levels. Of course water temp, CH, pH, and TA drive CSI, but for many, as long as they are within those acceptable levels, they are fine.
- We emphasize to members that they should use the PoolMath APP which further helps as well. Once an owner loads their pool info and submits water test results, the APP lets the owner know if there is a specific concern - to include CSI.

I guess what I'm saying is TFP does its best to reach a very wide audience. Our recommendations speak to that variety of pool ownership, but also has the ability to get deep into the weeds on certain topics as needed based on each specific set of circumstances.

 

[dws3]

Thanks to onBalance and Texas Splash for your explanations. I'll keep watching CSI and just make sure the contributing parameters are reasonable.