I may have finally found the reason for my high CH.

[LisaDLu]

My pool was replastered a little over a year ago and ever since then, the calcium hardness has been steadily rising until now it is 1000. I've posted a few times on the forum but no one has been able to help me figure out why. It's gotten so high that I am now going to do a reverse osmosis on it. The company came out to test the water and this is what they think is cause of the high calcium.

" The TDS and Conductivity readings are very high. When those parameters are combined with the low alkalinity it becomes a problem. Your actual "adjusted" alkalinity when
the cyanuric acid is factored in is 41 ppm. That is about 40% of what is recommended by the National Plasters Council. That is aggressive water that will pull calcium from the plaster and will eventually damage your plaster. The high TDS and conductivity are acting as interference with the ability of the chlorine to oxidize and sanitize."

They measured the TDS at 5580 and the Conductivity at 7144. I have been keeping my TA at about 60 (recommended for the SWG) but for the last few weeks it has been at 50. I'm wondering if I have been keeping the TA too low all along (I've been aiming for the 60-80 range recommended here but am usually near the low end of that). Does this sound plausible to you? All other factors that people suggest for the high calcium are not valid. Thanks!

 

[Richard320]

Too technical for me. Maybe Chemgeek or Joyful Noise will see this and chime in.

Have you tested your fill water? During the summer, my CH climbs about 25/ week due to evaporation and refilling. I'll bet you lose more water every week than me.

 

[jblizzle]

Post your actual test results from one of the recommended test kits.

TA being a little low is no issue if your CH is high.

 

[JoyfulNoise]

They are wrong.

The TDS and Conductivity readings are very high. When those parameters are combined with the low alkalinity it becomes a problem.

No, they do not. TDS is mostly an irrelevant parameter that is meaningless. As for conductivity, the reading is totally normal for an SWG pool. 7144 micro-S/cm conductivity is equal to ~ 3500ppm in NaCl units or about the perfect level of salt for an SWG pool. So right there they were either ignorant of the fact that your pool water is from a pool that uses an SWG or they simply don't understand what TDS/conductivity/salinity mean.

The ionic strength changes to the relevant chemical equilibrium constants are affected by TDS and salinity but these are factored in to Pool Math already. If you entered your chemical levels in correctly, then Pool Math accounts for the changes.

Your actual "adjusted" alkalinity when the cyanuric acid is factored in is 41 ppm. That is about 40% of what is recommended by the National Plasters Council. That is aggressive water that will pull calcium from the plaster and will eventually damage your plaster.

Adjusted Alkalinity is irrelevant. Alkalinity is alkalinity no matter the source. Cyanuric acid provides alkalinity to your pool water just as carbonate alkalinity does; it's just a smaller quantity. Once again, Pool Math adjusts all of the relevant parameters internally so that the CSI reflects an accurate picture of your calcium carbonate saturation. As long as your CH, pH, TA and CYA produces a CSI that is within balanced ranges (-0.3 to +0.3), it does not matter what the individual numbers are. So if your TA is low (like mine to keep the pH from rising too fast), then your CH can be higher and you can still have balanced calcium carbonate saturation in your water.

The high TDS and conductivity are acting as interference with the ability of the chlorine to oxidize and sanitize.

This statement, once again, demonstrates their ignorance. TDS and conductivity has absolutely NO impact on the ability of chlorine to sanitize.

I'm sorry that your water's CH rose so much as that is very unusual. However, plastering companies often don't understand the first thing about water chemistry and many of them do not even follow the NPC guidelines for proper plaster startup procedures. Plaster that is improperly cured and not started properly can emit calcium long after it is filled with water. My guess is, the CH rise you saw was due to an improper plaster startup and then unbalanced water chemistry and is the fault of the plaster company that redid your pool. However, without reliable test data and a complete record of the startup process used and chemicals added to the water, there is literally no way to know why your pool did what it did.

Going forward, my suggestion to you is this - once your water is RO'd to remove the high calcium levels, you should take control of your own water re-balancing by using YOUR test kit to measure the water and then post results here so we can help you. Do NOT let the RO company rebalance your water as they more than likely to just screw it up. What you choose to do is your decision.

Good luck.

Matt