pH jumping up more than usual...

[tuxedy]

Hi all, I tested my pool this morning:
ph: 8
FC: 5
CC: 0
CYA: 30
CH: 825ppm
ALK: 50
Temp: 21C

Here we have had a very dry season, basically no rain in the last 2 months with 45% humidity, maybe even less at times. Pool has slowly become more cloudy and slightly turquoise in shade. Did a OLCT last night which was 0. Usually I lose about 1.5-2 ppm per day depending on sun, but these days it's about 2.5 but sun is constant... seems okay. Filter runs 4 hours during the day and 1 hour at night when I add chemicals (cal hypo, only thing we have here).

So weird thing is that when my ALK was low like 30, I would never need to add any acid for weeks, maybe even 2 months, it would hover at 7.4. But in the last 2 months of intense sun the ph jumps up, I just added acid last week to 7.5 and it jumped to 8 in a week.

Mind you, our pool paint is microbubbling near the tile line and I think there maybe some algae hiding there, but since I don't have any OLCT do I need to do a SLAM or just run my pump longer since it's really dry and we live by dirt road so there is a lot of dust - (our patio and tiles are covered in dust each day)....

 

[mgtfp]

It's probably not that weird. Pool stores only tell you half the truth about Total Alkalinity, i.e. that it is used as a buffer to avoid pH swings. Which is true, and also important, especially when using acidic sources of chlorine like Trichlor, to avoid pH crashing down.

The other, outside of TFP often not understood side is this: Total Alkalinity gets adjusted by adding sodium bicarbonate (aka baking soda) to establish a carbonate buffer system. This basically means dissolving CO2 in the water to the degree where the water is oversaturated with CO2 relative to the CO2 in the air above the pool. This CO2 wants to outgass, in the same way that it wants to escape a bottle of soda water once opened. While outgassing from the water, pH rises.

So, with the "classic" targets for TA of 100-120 (which is required when chlorinating with Trichlor), pH is constantly on the rise when chlorinating with liquid chlorine or cal-hypo.

I'm surprised that you already see pH rising quickly with TA 50. That's actually the lower limit we recommend, the 30 you had was a bit too low and could result in pH crashing down. Around 60-70 most here achieve good pH stability.

CYA also adds to TA (about 1/3 of the CYA ppm counts as TA ppm), so if your TA was 30, then your water might actually have been under- or just saturated with CO2, depending on pH.

Have you recently been coming out of rain season? Do you get a lot of rain during rain season where you frequently have to drain water from the pool? And did you have to add more tap water recently to replace evaporation losses? Rain water basically has no TA, but tap water can be high depending on where it comes from.

Have you been adding sodium bicarbonate?

How are you testing TA?

 

[tuxedy]

Thanks for the questions. I test using the taylor k2006 kit. Overall TA would be more like 40 since there is 30 CYA (33% is -10 to the overall TA).

I do add water, usually once every week to two weeks during this dry spell. Usually it is pretty wet here the rest of the year, humidity averages like 65% and we get some pretty hard heavy rains for short periods of time. I was wondering if my problems have to do with my bubbled paint, which is now only 1.5 seasons in. Our pool is only that old, and when the acrylic paint was done the first time it immediately had small bubbles near the tile skim line. Those have somewhat burst but remain attached to the wall. At the base of some of the bubbles is a faint concrete surface that when I push on the bubble a small wiff of green comes out, which I know is algae. I just don't know if I need to repaint the entire pool again. The adherence of the rest of the pool is pretty good other than wear on the steps and streaks of paint loss due to the manual pool vacuum. Last time I slammed my pool it took 7 days, and in the past it would last a month - two months of super clear but this time it kinda got a bit cloudy and turquoise only after a week despite passing OLCT CC tests 2 nights in a row.

I haven't given it much consideration to do another SLAM since quite honestly, it's a lot of work. I'm not getting any overnight loss and I don't have any CC. when I reduced my FC from 8-7.3 it made a huge difference, though it took 1 Liter of acid to do it. I am expecting huge rainfalls in September that bring down all the pollutants in the air (I live in capital city of Rwanda) , and when it does the pool almost always goes really green and precipitated after a long dry spell like this, and will SLAM then. My question I have is that despite no OLCT and no CC, and having this cloudy appearance, does it mean I should just run my filter for a few days to try and get rid of the fine sediment from all the dust in the air, or do I need to SLAM it in order to cause the dust to aggregate better for my sand filter to filter it out?

 

[mgtfp]

Thanks for the questions. I test using the taylor k2006 kit. Overall TA would be more like 40 since there is 30 CYA (33% is -10 to the overall TA).

You don't have have to add it. Since this CYA-Alkalinity is real Alkalinity it shows up in the TA-test. That's why it's called Total Alkalinity - because it includes all types of Alkalinity, not just carbonate Alkalinity which is added via bicarb. I just mentioned that because with about 10ppm of Alkalinity coming from CYA, the carbonate Alkalinity which is responsible for pH-rise due to CO2-outgassing would have been only 20ppm.

I wouldn't let TA drop below 50. If you get that much rain then you might have to nudge it up from time to time.

A SLAM does nothing regarding dust, that's a filtration job. But if there is algae in those bubbles, that's different. It might be difficult for chlorine to actually get there. Do you get the algae out with brushing?

How big are these bubbles? I have never heard about acrylic paint as a surface finish on a concrete pool, especially not with a new build. Any hopes for warranty repairs?

 

[tuxedy]

Bubbles range in size from 1/4 inch to max 3/4 inch or so. My guy said he would try a different imported paint so we may do so but honestly wait another year since we haven't seen him try it on another pool.. we were the guinea pig for his first project in this country though he has other experience in South Africa.

The algae does kinda "poof" out with brushing... but too vigorous brushing starts to pull the tops of those bubbles off.