My makeup water quality is about 210 mg/l CH

[paetzoldb]

My makeup water quality is about 210 mg/l CH and after only 18 months since the pool was built/filled (two seasons) I have some areas of "discoloration" in my pool with a pebble finish. The pool builder brought out the finishing contractor. He took a sample and the one highlight that the pool builder pointed out is the high level of CH at 1200 mg/l. My testing puts CH at 925 mg/l and I have been a TFP follower since the pool was built with the CSI staying in the +/- 3 range with only some outliers with a high at +.48. And, even though I have no noticeable calcium deposits around the tile line he believes it is due to high CH. I believe since discoloration seems to be only in the areas that I add HCL that it is more likely caused by me adding HCL too quickly. Does anyone have any thoughts either way?

So, with my water makeup at 210 CH and with the extremely high evaporation rate of the Las Vegas, I will have to come up with a game plan to keep CH down to a value to is deemed acceptable for the pebble finish. Even though I can keep the CSI at acceptable values, should there be recommended max CH concentration?

Thanks,
Brian

 

[chem geek]

Re: Mysteries of CSI and CH

Welcome to TFP!

I presume you mean +/- 0.3 range for the saturation index. What are your other water parameters (pH, TA, CYA, TDS, Temp)? If the discoloration is only in the area where you were adding acid, then you are probably right that you added it too quickly without proper mixing/dilution and it could have pooled and dissolved some of the finish. I would think that dissolving of the finish vs. buildup of scale would be distinguishable, especially by the finishing contractor. Pouring slowly over a return flow and then brushing the area where you've added the acid to ensure thorough mixing is the safest approach.

As for a max CH, it's really going to come down to what the pool builder is going to warranty, assuming there is any sort of repair that is done. If he wants you to have a lower CH level, then you'll have to dilute the water to do that. Note, though, that with your SWG your positive saturation index may result in more scaling in the salt cell unless you are using 50 ppm Borates.

 

[duraleigh]

Re: Mysteries of CSI and CH

should there be recommended max CH concentration?

Yes. There are maximum and minimum suggested values for all the important parameters (including CH). CH should be between 250 - 400ppm.

Of course, you can deal with somewhat higher values but if you keep your other parameters within the guidelines we suggest in Pool School, you won't have to worry about scaling. (or CSI, for that matter)

What are your other test results for pH and TA? What is the CH of your fill water?

 

[JasonLion]

It is very important to pour acid rather slowly and only while the pump is running, preferably pouring directly in front of a return jet so it mixes in as quickly as possible. Failure to do this correctly can result in etching of the plaster between pebbles, but would not result in the buildup of calcium deposits.

It is generally possible to compensate for high CH levels only when CH is below about 1,000 to 1,200. With CH above those levels there will almost invariably be times when you get calcium scaling despite your best efforts to keep CSI under control. Even with CH around 900 to 1,200 it requires quite a bit of care and careful attention to maintaining appropriate PH and TA levels to prevent scaling.

In situations like yours, it is common to lower the CH level back to something quite low every year or two, either by massive amounts of water replacement or by getting a reverse osmosis treatment. The CH level of your fill water likely varies over the course of the year and some people find times of year when fill water CH is low and do their water replacement then.

 

[paetzoldb]

Thanks for the input all. My current readings: Temp 50 deg, FC 0, pH 8.0, TA 100, CH 925, CYA 80, Salt 3200, Borate 60-70 (in between 50 and 80) and this gives a .24 CSI (yes I did miss the "." for .3 earlier). I tested TDS today and it is at 4650 ppm. During this last summer I would try to maintain pH around 7.6 to 7.9 since the pool temp would achieve 88 deg and CH was at 600 during the second week of July.

Make up water: pH 7.9, TA 120, CH 210

Dave, I wished I did not have to worry about CSI but I cannot see where that is a viable option short of having a RO to maintain the daily water evaporation. In Las Vegas evaporation is just under 1"/day or about 300-400 gallons/day for my pool during the three hot months. BTW, keeping an eye on the CSI is no issue at all with the iPhone and The Pool Calculator...extremely easy.

As far as pouring the acid, I thought I was mixing it safely since I would only pour it in the areas that was currently being agitated by the in floor cleaning. After adding acid I would continue to mix for about 1 hour (egg timer feature in Pentair).

I will be lowering the water level to a bench area that I see the discoloration and we (pool builder will come back over) can look at the surface without water. I will give feedback next week for the record. For the future I am thinking that I will be keeping my CH lower (max 800?) to ensure I have plenty of margin for the heater and SWCG.

Thanks again.

 

[duraleigh]

Dave, I wished I did not have to worry about CSI but I cannot see where that is a viable option

In my view, it is quite easy to do. Simply maintain your pH down around 7.2 and your TA around 90ppm (towards the bottom of the suggested acceptable ranges) and that will compensate for the CH being high. Then, as your CH continues to drift upward, you will have to introduce some replacement water but you have to do that now, anyway.

There are a number of folks here on the forum that manage scaling in that manner.

BTW, your pH is currently a little too high. It should not be allowed to go beyond 7.8 even in a pool that does not have the calcium issues you have.

Even at a pool temp of 50 degrees (really? In Las Vegas?) I would suggest you maintain a little chlorine in the pool. I keep mine open all winter here in NC and find I still need 2ppm or so of chlorine to keep the pool sparkling.