Why does CH go up?

[drummerman951]

Was going to hold off for a bit on the drain to lower CH, but over the last two weeks my CH is just about 450 now. I know many people wait longer to do a partial drain.... but I'm wondering what causes CH to rise in the first place.... besides adding calcium or salt to the pool.

Today I'm going to embark on water exchange.... PoolMath says that I need to replace 32% of the pool to drop to 350. Based on refill water of 160 CH. Not sure I want to do that all at once. I think I'm going to just run the sump pump for an hour, test CH and repeat. An hour should clear roughly 3500 gallons, but now I get to use my handy flow meter as well.

I calibrated it as best as I was able, although mfg recommends using 50 gallons for precise measurement. That's a lot of 5 gallon buckets!
Here's the link for those who may be curious. I looked at many cheap ones on Amazon, and with a tolerance of +/- of 20%, too much error for me.

Digital Water Meter - Totalizer and Flow Rate DM Series

What is really bugging me is that I have no idea why CH is rising. My test results in PoolMath are linked from my profile.

 

[Richard320]

CH rises because water evaporates but Calcium doesn't. Fill a pan with tap water and set it in the sun to evaporate. Then take a look at that white crust. There's your CH.

450 CH isn't that bad. That's actually close to the lowest my pool has ever been. It's not too difficult to maintain a decent CSI up to about 800 CH. You just need to keep the TA low and maintain pH at the low end of acceptable. Plug your numbers into poolmath. Then watch CSI as you raise and lower pH, TA, CH, and temperature. Even salt. CH has a lot less effect on scale formation than you think. Don't just plug an arbitrary target into poolmath. What if the fill water later in the summer comes from a different source, with 250 CH? You'll be replacing water almost continuously if you keep the target at 350!

When my CH starts to get around 800, I empty the spa into the pool and then use pool water to water the lawns while I refill the spa. You've got a salt system, so that might not be such a good idea.

 

[mknauss]

Calcium is a dissolved solid. When water evaporates from the pool, that solid stays in the remaining water. Then you add 160 CH fill water to replace what evaporated. Your overall CH rises.

I would not drain/exchange any of your water for a CH at ~450 ppm. That is not significant. By learning how to manage CSI you can manage your water scaling tendencies pretty easily up to a CH of 800+. Even higher with more advanced techniques.

It appears you are using a 25 ml water sample for testing CH. Use a 10 ml sample, and each drop of reagent to blue will be 25 ppm CH.

 

[drummerman951]

Thanks for explaining CH to me. Why is the TFP CH guideline 350-450 if we can go up to 800-1000 before partial drain? I know the Taylor APSP reference chart says 200-400 optimal (I'm assuming these numbers for chlorine pool); max 1000, but I'm conflicted being at the top end of TFP scale..... with visible scale around pool tile and what not.

Do you think that having pool service once a week previously allowed scale to occur due to very high pH occurring between services?

 

[mknauss]

The TFP ranges are built so if one can stay within them, there is no need to be concerned about the more technical aspects such as CSI. But in our area of high CH and TA fill water, we cannot reasonably stay in all the ranges. So we learn how to manage our water using another tool, CSI.

High pH and TA are the worst offenders for scale creation. Up to that 800+ CH range, you can easily manage CSI by keeping pH in the 7's and TA under 80 or so. It is not likely a pool service will do that - as that is not possible with the dump and run business model.

 

[drummerman951]

The TFP ranges are built so if one can stay within them, there is no need to be concerned about the more technical aspects such as CSI. But in our area of high CH and TA fill water, we cannot reasonably stay in all the ranges. So we learn how to manage our water using another tool, CSI.

High pH and TA are the worst offenders for scale creation. Up to that 800+ CH range, you can easily manage CSI by keeping pH in the 7's and TA under 80 or so. It is not likely a pool service will do that - as that is not possible with the dump and run business model.

Hi Marty... so my CH is over 600 now... and I'm waiting to do any drain until 800-1000... I'm trying to keep pH ~7.4 so my CSI doesn't go below -0.30... my daily pH results are almost always 7.6 and I add 16oz acid daily. Should I be doing anything else to properly manage rising CH? TA is usually 70-80. Water looks great. Thanks for your advice!

 

[mknauss]

No -- just manage your CSI. Test your CH every month. It will go up some each month.

 

[Rancho Cost-a-Lotta]

I know they're kind of a pain, but a solar cover would reduce evaporation and, in turn, reduce the amount of calcium added to the pool via fill water.

 

[drummerman951]

I know they're kind of a pain, but a solar cover would reduce evaporation and, in turn, reduce the amount of calcium added to the pool via fill water.

I agree. I have one. But the weather has been nice lately and family uses the pool every day. I just can't bring myself to put it on and take it off everyday. Especially because its not very flattering to sparkling pool water.

 

[Rancho Cost-a-Lotta]

I agree. I have one. But the weather has been nice lately and family uses the pool every day. I just can't bring myself to put it on and take it off everyday. Especially because its not very flattering to sparkling pool water.

I totally understand.

 

[Miniguy77]

CH rises because water evaporates but Calcium doesn't. Fill a pan with tap water and set it in the sun to evaporate. Then take a look at that white crust. There's your CH.

450 CH isn't that bad. That's actually close to the lowest my pool has ever been. It's not too difficult to maintain a decent CSI up to about 800 CH. You just need to keep the TA low and maintain pH at the low end of acceptable. Plug your numbers into poolmath. Then watch CSI as you raise and lower pH, TA, CH, and temperature. Even salt. CH has a lot less effect on scale formation than you think. Don't just plug an arbitrary target into poolmath. What if the fill water later in the summer comes from a different source, with 250 CH? You'll be replacing water almost continuously if you keep the target at 350!

When my CH starts to get around 800, I empty the spa into the pool and then use pool water to water the lawns while I refill the spa. You've got a salt system, so that might not be such a good idea.

Is there any problem with using pool water on the lawn, given the usual amount of FC in the pool?

 

[gonfishin]

Is there any problem with using pool water on the lawn, given the usual amount of FC in the pool?

Admittedly, I think I have more weeds than grass in my lawn, but I've seen no adverse effects of using pool water on the lawn. Unless you count grass growing faster

 

[Richard320]

Is there any problem with using pool water on the lawn, given the usual amount of FC in the pool?

I haven't seen it.

The salt that the bleach leaves behind hasn't affected things either as far as I can tell.

What I did notice is the weed seeds (dandelion in particular) that get caught in the filter like to take root where the backwash water goes. I backwash to the street now.