PH drift issues - help please!

[CDJAZ]

1. Background. I emptied, cleaned, and refilled my hot tub (300 gallons) in fall. We did not use it almost at all since then, and I didn't really maintain the chemicals. Now my wife decided she wants to start using it again. Last week, I did all the tests, balanced the water and she went in. She complained of it feeling like sandpaper. Darn. I read up and I guess that is what we call scaling? Makes sense because my PH was through the roof. Started doing some reading and found the sticky here 'how to maintain my hot tub with chlorine'. Perfect! Just what I was looking for.

2. What I did.
a. My calcium hardness was super low. I brought it up to 120.
b. My TA and PH were both super high. I brought the PH down to 7.0 about 5 or 6 times until my TA is now 50.
c. My FC was low but not quite 0. I have been keeping it between 3 and 6.
d. My wife scrubbed the entire hot tub to get rid of the 'sandpaper'

Most recent test results:
a. FC 0.8 (added to bring to 6)
b. CC 0.4 (ok)
c. PH 8 (added 9 grams/0.3 ounces of PH-)
d. acid demand test, 1 drop.
e. TA 5
f. Calcium 120

3. Where i'm at, what I need help with.
a. Every time I test it now, the PH is 8 but the 'acid demand test' that comes with my test kit only calls for like 9 grams of dry acid. I know, I should start using muriatic acid now that my TA is at 50 but I don't have any with me so Why is it still drifting up so fast? How do I stop it from drifting so fast?
b. There is like a yellow scum that is sort of loosely floating at the bottom of the seats? What is that?
c. Should I be worried about any scaling that would have taken place inside the piping? If so, what do I do about it?

p.s. this site has been such an awesome resource for me to take care of my pool. It is so easy, I didn't expect the hot tub to be so much more work! Thanks all!

 

[mgtfp]

What were your water parameters before you readjusted them? It sounds like your CH was really low and you added calcium chloride to increase it to 120ppm. If it was really much lower than 120, then your TA and pH must have been really high to get into scaling territory. Just trying to get the whole picture before starting with diagnosis.

 

[CDJAZ]

What were your water parameters before you readjusted them? It sounds like your CH was really low and you added calcium chloride to increase it to 120ppm. If it was really much lower than 120, then your TA and pH must have been really high to get into scaling territory. Just trying to get the whole picture before starting with diagnosis.

My readings when I started:
FC = 0
CC = 0
PH = 8.0 (max reading)
acid demand test was 7 drops = 65 grams of dry acid
TA = 200
CH = 100

It was sitting at these levels for quite a long time without me looking at it since we weren't using it.
I started with calcium chloride to raise CH, 65 grams of dry acid, and whatever dichlor to get my FC up (my CYA was at 0).

I added PH- probably 6 or 7 times over a period of 5 days. My TA has come down as expected but my PH doesn't want to come down. The amount of acid it's calling for to bring the PH down to 7.5 is now really low but when I add it, the PH bounces right back up immediately (within 30 minutes, 1 hour)

thanks!

 

[mgtfp]

I guess, if your pH was at or above 8, and the water warm enough, then scaling could indeed have happened. What was the water temperature like?

To confirm that this is really calcium scale, you could collect a small sample and add a drop of acid. Calcium scale should start to fizz.

Not sure about that yellow scum, I'm not experienced with spas. But from what I read here, spa users swear by a product called Ahh-Some to get rid of biofilms and other gunk. Maybe someone more experienced with spas like @jseyfert3 will chime in.

 

[jseyfert3]

b. There is like a yellow scum that is sort of loosely floating at the bottom of the seats? What is that?

I've never seen yellow scum in my spa, but with a spa setting filled (and presumably heated) with no chlorine chances of biofilms building up are high. When we bought our house it came with a hot tub that was filled and warm, and presumably fairly ignored. I did an Ahh-Some purge and got some nasty junk coming out. However, biofilm won't affect pH rise, just chlorine demand.

3. Where i'm at, what I need help with.
a. Every time I test it now, the PH is 8 but the 'acid demand test' that comes with my test kit only calls for like 9 grams of dry acid. I know, I should start using muriatic acid now that my TA is at 50 but I don't have any with me so Why is it still drifting up so fast? How do I stop it from drifting so fast?

I'm assuming you have a Taylor K-2006 or equivalent? Are you doing the test with a 25 mL sample size so you get a 10 ppm drop resolution? And are you going till the color stops changing, then not counting the last drop that didn't change the color any further? It's not very clear in the instructions, when I first started I stopped at the first hint of red, leaving me to believe my TA was 50 when it was actually 70 or 80.

If that's all squared away I'm not sure why your pH is rising so fast still. Are you adding anything besides dichlor and dry acid?

Borates can help slow pH rise, but it'd be nice to figure out why your pH is rising this fast before you add borates. I've been meaning to add some to my spa, but have not. I don't have the immediate pH rise you are seeing. Still rises, but not that quick. As outlined you can get boric acid which is closer to pH neutral or you can get borax from your local grocery store, which will require adding acid to counter the pH rise. PoolMath will calculate the approximate amount of acid you need to counter pH addition from adding borax (but it calculates the acid addition as 31.25% muriatic acid).