CYA is in check but CH continues to rise

[sharper4]

I have a newly built plaster pool and have been following the BBB method. I have noticed that my CYA seems to stay in check (with normal splashing it'll actually fall so I periodically use a tab or two every so often to keep it in the 40-50 range). As I look back at my chemical log I'm seeing that my CH is trending up (up to 344 from 276 3 wks ago). Anyone have any ideas why? At this trend it'll be out of optimal range here in the next week-ish.

Latest results:
FC: 3.5
pH: 7.8
TA: 97
CH: 344
CYA: 35

I did throw a tab in the chlorinator this week to bring the CYA up a little. I might throw a second in to help get it closer to 50.

 

[Smykowski]

Have you been topping off due to evaporation? Have you ever tested your fill water? What are you using to chlorinate?

 

[jblizzle]

Could be due to evaporation ... or have you been using any cal-hypo?

What are you using to test with as your TA and CH numbers have too many significant figures?

 

[Patrick_B]

New Plaster is going to raise calcium too.

 

[sharper4]

I use the 2006 kit, its one of the recommended ones here. I also take it to the store for verification ... they're usually pretty close on most numbers. I do top off due to splash out and evaporation about once a week.

When the pool was first filled the CH was 276. I don't know what the tap water has in it but since it was first filled with tap I would presume its gotta be close to the 276-ish number.

I use bleach to chlorinate via the BBB method unless the CYA gets below 40 ... then I stick a couple tabs in to bring CYA back up into range and then use exclusively the BBB method again.

 

[duraleigh]

1 tab in your pool raises your CYA by about 2 ppm. You need to get more precise in your dosages so they do what you expect them to.

If you have a K-2006, taking the results to the pool store to "verify" usually "un-verifies" your work. You must learn to trust your own testing.

Test the CH of your fill water.

 

[sharper4]

OK - I will test the fill water. And I'll trust my own results a little more. I'm going to guess the fill water CH is lower than the pool's right now. Is the only way to lower the CH by replacing water? Any thoughts on what's causing it to rise?

 

[jblizzle]

This is why it is rising:

Could be due to evaporation ... or have you been using any cal-hypo?

Only 2 ways to lower CH: Replace water with lower CH water, Reverse Osmosis treatment (very limited markets and not cheap).

 

[Isaac-1]

I suspect this is due to a combination of high CH fill water, probably high rate of evaporation although you do not say where you live, and new plaster in the pool.