pH Insanity - Constantly Rising + Test Differences

[Tubber99]

I've had my bromine-based tub for about a two weeks and since getting the pH, TA, CH, and bromine in line, I've had daily pH rises that I am unable to stop. I had 2 different kinds of test strips + a phenol red kit - typically the drops are showing a higher pH than the strips; in fact, often times the drops will show red/8.2+ (filling to the fill line + adding 4 drops + inverting as per the instructions) and the strips will show somewhere in the mid to high 7s. I had my water tested yesterday and it came back as follows:

pH: 7.2
TA: 73
CH: 127
Total Bromine: 5
TDS: 700

They suggested adding 9.75 tablespoons of SpaGuard Balance Pak 100 to hit their suggested TA of 125-150. My manual suggests that 80-120 is acceptable. I added 4 tbsp of baking soda, which increased my TA (it looks like it is around 70 now after more reducer was added). Checking the hot tub this morning, the pH is once again showing 8.2+ using the phenol red and in the high 7s using the test strip. This has been a daily occurrence over the past week, save for yesterday when I added baking soda. I find the phenol red is all over the map - almost as though the red color if affecting the water color rather than the reaction - I tried two tests this morning, one was 8.2+ and the other was around 7.7 - difference was adding 2 drops and inverting then adding another 2 and inverting vs adding all 4 at once and inverting.

I've heard people of both sides of the fence - get your TA in line and then adjust your pH vs. a low TA (60+) is fine, just control your pH. I do have an ozonator and noticed a decent amount of bubbles coming from the other jets when the filter runs. Could this be enough the be raising my pH daily? Should I try to spike my alkalinity by putting in ~10 tablespoons of baking soda + aerate? This will undoubtedly raise my pH, which could be brought down by using my pH reducer (using Aquarius pH Reducer - granular from Canadian Tire), but I'd rather not add a pile of both substances if it is not necessary. Or am I doomed to needing to add pH reducer on a daily basis?

 

[waterbear]

First, get a GOOD drop based test kit and start testing the water yourself. I would recommend a Taylor K 2106 for bromine, which uses the FAS-DPD bromine testing method, a pH test that will accurately test pH up to about 20 ppm Total Bromine, along with both acid and base demand tests so you know exactly how much product you need to ad to adjust pH, and drop counting tests (titirations) for both TA and CH. It's not exactly cheap but neither was your spa so don't skimp on the test kit.

On 11/4/2020 at 2:26 PM, Tubber99 said:

a phenol red kit - typically the drops are showing a higher pH than the strips; in fact, often times the drops will show red/8.2+

My guess is that this is a known interference with phenol red and high sanitizer levels where a purple red color develops instead of the normal color range of phenol red and in inexpensive kits can happen when bromine is as low as 5 ppm. The fact that you said you needed 4 drops tells me this is not a Taylor kit but one of the inexpensive ones that probably also uses OTO testing for bromine (comparator is shades of yellow for sanitizer).  The only difference when adding 2 drops of pH reagent vs 4 would be the intesity of the color, not the shade, btw.

THE MAIN CAUSE OF pH RISE IN A POOL OR SPA IS OUTGASSING OF CO2.

THE HIGHER THE TA (CARBONATION IN THE WATER), THE FASTER CO2 WILL OUTGAS AND THE FASTER THE pH WIL RISE.

THE HIGHER THE AERATION OF THE WATER (OZONE SYSTEMS, SALT WATER SANITIZER SYSTEMS, AIR INJECTORS,  AERATION FROM YOUR JETS, 24 HOUR CIRCULATION ON HIGH SPEED, ETC.) THE FASTER CO2 WILL OUTGAS AND THE FASTER THE pH WIL RISE.

THE LOWER YOU PLACE THE pH THE FASTER IT WILL RISE (YOU ARE CONVERTING MORE BICARBONATE IONS, WHICH IS WHAT TA IS,  INTO CARBONIC ACID, ESSENTIALLY CO2 DISSOLVED IN THE WATER

As far as pH and TA you want to adjust the TA to desired level (50-70 if you are having a problem with pH rise and are using bromine tablets, since they will tend to lower TA and pH over time) and an ozonator (which will speed the outgassing of CO2 which causes pH rise) and then adjust your pH to the desired target. Bromine is active over a pH range of about 7.0 to 8.0 so it's not as critical as it is for a chlorine spa.

This post explains how outgassing causes pH rise and how to minimize it.

https://www.poolspaforum.com/forum/index.php?/topic/28846-lowering-total-alkalinity-howto/