Disappearing Calcium

[etbrown4]

10k fiberglass pool. Have all chems in the correct range except calcium hardness.

30 days ago it was correct at 300, however today it is 0.

What could be causing calcium to drop so rapidly?

 

[JamesW]

It's not 0.

Probably test error.

 

[JamesW]

 

[etbrown4]

Ok its way low.
What can cause calcium hardness to drop so rapidly? Like to hear from those who have experienced this specifically with a fiberglass pool.

 

[JamesW]

What is the exact number?

What is the CH of the fill water?

Most likely a test error or test interference.

Test the fill water.

Copper will interfere with the test.

Maybe a leaking autofill.

Other than dilution, there are not too many ways to lose calcium.

Adding a bunch of Trisodium Phosphate can drop out calcium as calcium phosphate.

 

[JamesW]

If the problem is dilution, your CYA will also drop to 0.

If the CYA is the same, then the problem is probably test error or interference.

 

[etbrown4]

Back to the original question, just want to see if fiberglass pool owners have see dramatic drops in calcium hardness, like i have experienced.

Years ago with another FG pool i did see where the hardness impacted a disintegrating gel coat, though I have not observed chalking of the fiberglass surface this time.

 

[mknauss]

The only way calcium hardness leaves the pool is to exchange water. So it is likely you have testing error.

Modern fiberglass is not effected by low CH levels.

 

[JamesW]

Back to the original question, just want to see if fiberglass pool owners have see dramatic drops in calcium hardness, like i have experienced.

Three ways to lose calcium.
1) Dilution.
2) Precipitation from added Trisodium Phosphate.
3) Reverse Osmosis.

If none of those things happened, then you probably have test error or test interference from copper or other metals.

Can you post a full set of readings including salinity from a K-1766 salt test kit and salinity from a good salt meter?

 

[etbrown4]

Will re-read CH tomorrow and add calcium if indicated, and read again.

 

[mknauss]

Where are you located? What is the CH of the fill water you use?

 

[etbrown4]

CH reading is in range so sure enough it was a testing error.

That notwithstanding, over the past two decades I've personally encountered three 'modern' fiberglass pools with chalking gel coat. Some chalking so badly they would plug a high capacity sand filter in a few hours. Backwash was white. Each had very low CH.

The cure in all three cases was to raise CH to over 200 and in each case the chalking promptly ceased.

Though not on this esteemed forum, I've seen numerous posts from pool owners and those chemistry knowledgeable, who have identified the tendancy of low CH pool water to attack certain gel coats in order to obtain calcium.

I'm sure there may be some disbelievers, but it's hard to argue with consistent results. Not suggesting others try it, but simply sharing what I have seen work.