Supply to Spa - PH drops from 8.0 to 7.0

[frogabog]

For reference, I have posted in spas for my dad's octagonal orange hot tub here dad-s-spa-refilled-last-week-and-just-refilled-again-t35175.html

Dad refilled his 110+ CYA (in two weeks) spa today. The supply line is copper. Same as the whole house.

Kitchen tap PH is 8.0 which is what the water bureau intends it to be.

Test in the spa after about an 8-10 minute fill is 7.0 - It might be 6.9. I swear, I tested it within 15 minutes of starting the fill.

What the heck could cause this? Dad says the ph is always low. He's always raising it.

Now I figured the rain around here was lowering my ph. He has no rain. The spa is fully sheltered against all weather, although not entirely enclosed.

Thoughts?

 

[anonapersona]

Unstable pH? Low TA. Test to find out.

 

[frogabog]

Went to check the spa today. I made a huge mistake in calculations likely due to the fact that I was rushing to get out of there yesterday (fail) and put 6oz of dichlor in when I was supposed to put .6 oz.

OMG CYA was up to 60 today and the chlorine level was through the roof, I stopped when I got to 35ppm on the DPD. MAJOR DOH! I let it circulate and brushed algae off the bubble cover dad uses to keep the heat in, and soaked it in the spa... till dad told me he had more/new that just needed to be trimmed. I figure the major shock was a good thing and and it might have cleared out the system a bit.

So... we did another drain, this time about 60%. Upon filling I tested the actual fill water before it hit the pool. Right on for city tap water PH at 8.0. So it is NOT in the plumbing.

That leaves the pool itself, or the filtration system suspect. The green slime (copper obviously) on the filter has been cleaned off. Could that cause it? Would the "scale" on the walls do this? I don't know what kind of scale it is, it's kinda brownish but it's hard to tell because the spa is orangish. The "white" plastic parts such as the skimmer, are creamy with brown stains however.

TA for fill water was 10. TA in the pool was 40 after filling. I adjusted it to 50ppm w/2tbs plus 1 tsp of baking soda.

Added calcium to 130ppm. I still have a massive bucket of calcium left.

Final TC and FC was 7.5ppm. No CC. Much better than 35.

Adjusted ph to 7.4 from 7.2. Dad has a large bucket of PH Up, so I used that. He had adjusted it last night, but his method is to throw some in, check, and then throw some PH Down in cuz it was too high. I did not do that, pool calculator all the way with particular attention paid to where the decimal point is this time.

I assume the ph will continue to fall like it always does, but it would be best to find out why. Bear in mind, this is a very old spa. Orange octagonal w/tiles at the water line. I got it from someone about 19 years ago from their house boat dock, it sat upside down in my yard for about 10 years, then I gave it to dad who then spent a fortune and countless hours making it work for him. He added ozone, a monster sta rite cartridge filter, a monster heater, and a monster pump. Monster means HUGE. Overkill, but apparently it works.

Any ideas are welcome.

 

[Bama Rambler]

With a TA of 10 it's no wander that the pH stayed low. I'd raise it to about 70 without borates or maybe 60 if you have borates.

 

[frogabog]

Duraleigh's post in the other thread told me to do TA at 50.

PH this am was 7.4. Exactly what I aimed for.

FC 1.5 this am however. Seems like a large drop to me.

He is texting me from his spa w/results.

CYA 30

 

[Bama Rambler]

If 50 stabilizes the pH then it's fine, if it doesn't, then raise it some.

 

[frogabog]

OK, thank you.

He says water feels great. shrug...

 

[chem geek]

TA for fill water was 10. TA in the pool was 40 after filling. I adjusted it to 50ppm w/2tbs plus 1 tsp of baking soda.

With a TA of 10 it's no wander that the pH stayed low.

The TA of 10 was for the fill water, not the pool which was initially at 40 ppm but was later raised to 50 ppm. The low TA of the fill water would make it have even less of an influence on the pool's pH. If the spa was made of wood, then tannins could lower the pH.

 

[anonapersona]

Chem geek, if the TA was low and there was any event that would lower pH, like tannins from leaves or wood, wouldn't pH go dramatically low due to low buffering? (chemistry was always a mistry to me, the rules seemed so arbitrary)

 

[chem geek]

Yes, if the TA of the spa water (not the fill water) was low, then anything that can affect pH such as tannins could change the pH. So for a completely fresh fill using low TA fill water of 10 ppm, then I could see a large pH change, but if adding some 10 ppm TA water to a much larger body of 40 or 50 ppm TA water, the pH should not change very much. Maybe I'm not understanding the original question in this thread -- if it is that the pH drops a lot on a completely fresh fill using fill water with a TA of only 10 ppm (which would be very unusual, by the way), then yes, I can see that the pH could change a lot rather easily.

 

[frogabog]

The fresh fill was when ph was so low. The partial fill did not alter the PH at all.

The original question was regarding how a fresh fill with known PH of 8.0 could become 7.0 in less than 15 minutes.

When I test TA here at my house at the tap it's 40ppm. Yesterday I tested dad's at 10. Same source, same city. I dunno what happened, but I used R-0007, 8, and 9 for this test and it very clearly turned red with one drop.

There is a wood deck surrounding the spa, but it does not touch the water. The water filled up quickly, and nothing was put into the water before I tested. It was slightly shocking to say the least to see it fall so much.

I assume I'll get some spa texts tomorrow morning (dad is a daily spa wake up guy) with report on levels. I also think he ordered a DPD test kit from TFTestkits today because he asked for the link again. Showed him how accurate it is as compared to his K-2005. Now no one will use the 2oz R-0001 and 2 reagents I bought last summer.