New spa, second fill... Learning curve help

Insaneoctane

Member
Jan 12, 2021
6
Los Angeles, CA
I received my Bullfrog spa in November. As a previous pool owner, I thought I knew what I was doing. Now I know that I most certainly don't! After adding too much chlorine and shock to my first fill, I ended up draining it and starting over after only 2 months. I had gotten the CYA very high from over use of chlorine and things got really whacky. So I started over about 2-3 weeks ago, fresh fill.
Post fill numbers:
FC 0.11
pH 8.0
TA 99
CYA 5
So I added a pint of spa stain & scale (per Leslie's advice)
2 tbsp pH down
1 tbsp granulated chlorine

So, I was dialed at the beginning of the year. I was intent on NOT over adding chemicals this time!
I've done a good job of not letting the FC go to zero.
I've been adding MPS non-chlorine shock after every usage.

My challenge is I'm seeing the pH drop multiple times (4) in the past few weeks. I've been adding a tbsp of pH up each time to fix the problem. The ONLY chemicals I've been adding is enough chlorine to keep the FC in range (5 tbsp total in few weeks) and a fair amount of MPS @ 7 tsp per bather hour (24 tbsp total in few weeks). I'm surprised that I've had to raise the pH four times (almost twice per week). Is it because I'm over using MPS? Any advice welcome!
Last test:
FC 5
pH 7.2
TA 100
 

BigD23

Member
Jun 7, 2020
10
Richmond, VA
What granulated chlorine are you using? I'm guessing it's dichlor, and using dichlor will raise your CYA. As CYA gets higher it "reserves" more of your chlorine instead of letting it act, that's why you don't want the CYA level too high. I did this many times (using dichlor only then having to refill because I couldn't get it clean) until I discovered this site and the dichlor-to-bleach method.

I'm not as advanced as others in the chemistry, someone will probably know why your pH is dropping.
 
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Insaneoctane

Member
Jan 12, 2021
6
Los Angeles, CA
Spa Choice
It's 99% dichlor with 55.5% available chlorine.
I know it contains CYA, so I'm trying not to overuse it...
I've read that ANY shock product will lower pH. Wondering why that is and if I should be using less MPS?
 

Insaneoctane

Member
Jan 12, 2021
6
Los Angeles, CA
OK, per that link:
Although, as long as you're not adding Acid (or anything with a lower pH) to your tub, the pH will not usually drop....
....
Let me repeat the last sentence, because it's the single most important thing to keeping your water balanced. The key to having balanced water, without pH drift, is having the correct TA level..... If you find your pH is too low and/or your water is continually acidic, your TA is too low and needs to be raised. By fine tuning your TA, you can get your pH perfectly balanced, that rarely needs adjustment.
While my TA doesn't seem low at 100, I keep having to raise pH. I'm also not adding acid.
 

Mdragger88

Bronze Supporter
Jun 1, 2018
1,467
Hernando, Ms
If you’re using dichlor it will definitely lower ph. You may use this to your advantage. I have no clue about mps as is i don’t use it due to it’s absence in PoolMath
Use effects of adding to determine the consequences of additions
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jseyfert3

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Oct 20, 2017
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Also:

So I added a pint of spa stain & scale (per Leslie's advice)
We don't recommend listening to Leslie or any other pool store's advice. There advise often requires you to buy something from them. Coincidence? Nope. Why did they recommend that? What is your CH level, you did not list that.

2 tbsp pH down
Wondering why that is and if I should be using less MPS?
Dry acid (sodium bisulfate, which is what pH down is), and MPS (potassium monopersulfate) contain sulfates. Sulfates will speed up corrosion of your heater. There's nothing wrong with using them, just something to be aware of. An alternative to dry acid is muriatic acid (hydrochloric acid, or HCl), and is recommended here. However the full strength 31% does fume, and more caution is needed when using vs dry acid. You can also get the "green" muriatic acid, which is general half strength or ~15%, which has much less fumes.

MPS can be useful to add after using the tub to break down waste and help avoid the formation of CCs. Due to the sulfates it adds its use should be kept to a minimum needed to avoid the formation of CCs if used. Note it will also affect the FAS-DPD test for FC/CC unless an interference removal reagent is used.

Does your tub have ozone and/or UV? I recommend you fill out your signature with your spa model/gallons, any UV/ozone/saltwater chlorine generators, and what you use to test. https://www.troublefreepool.com/account/signature
 
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Insaneoctane

Member
Jan 12, 2021
6
Los Angeles, CA
I'm very surprised that MPS is absent from pool math as MPS is fairly common in spas?

I have no ozone/UV/generators just me trying to keep things balanced. I've been using test strips, but am ordering either TP-100 or K-2006C per this site. I'm interested to see how high my CYA is. I probably should switch to bleach vs dichlor, but I'm still studying!

Adding 1/2 cup of MPS after 4 bathers have spent an hour in the hot tub seems like a lot of product. I'd like pool math to help me understand the effects of 1/2 cup of MPS! Maybe I should stop shocking with MPS after every use, but if need a better alternative.
Thanks for the replies. I'll post what my CH values were in a bit...
 

jseyfert3

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Adding 1/2 cup of MPS after 4 bathers have spent an hour in the hot tub seems like a lot of product. I'd like pool math to help me understand the effects of 1/2 cup of MPS! Maybe I should stop shocking with MPS after every use, but if need a better alternative.
As I said, some MPS can be good. You should try to use the minimum needed to accomplish your goal though. Where do you get 1/2 cup after use?

I haven’t used MPS myself before, but from the aforementioned sticky:
If you find you're having trouble keeping FC in your tub during parties, and/or you smell a foul odor during your soaks, you can add Potassium Monopersulfate (MPS or Non-Chlorine Shock) before (and/or during) your soak to help the Chlorine Oxidize waste. The only thing I would say is, go easy with MPS. Use only the amount needed and not much more. It is acidic and will lower your TA/pH if you use a lot. Start out with 1-2 tbs in addition to your normal FC, and see if that cuts down on the FC usage. Up it to 3-4 tbs, or add another 1-2 tbs during the soak if needed. MPS will help oxidize waste. However, it will not kill bacteria, so you still need FC. Also, you can use MPS as a shock once a week to help oxidize leftover waste, and reduce Combined Chlorine (spent FC).
 

jseyfert3

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I'm very surprised that MPS is absent from pool math as MPS is fairly common in spas?
It’s not as common on TFP. It is possible to manage a spa with chlorine only, especially if it’s outside in a sunny location you can open the lid and get some UV from the sun once in a while. If it’s not possible to do that and you don’t have UV or Ozone then CC buildup may become an issue depending on how much you use the tub, and it’s here that MPS can help by breaking down waste before chlorine so you generate less CCs.

Also TFP is primarily focused on pools, since there’s a lot more pools than spas out there, so a lot of the stuff including PoolMathis geared more towards pools, but most is applicable to spas still.
 
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