Dichlor Then Bleach Method with High Fill TA

[DanF]

I have started using the dichor-then-bleach method when draining and refilling my spa. The issue I face is that my fill TA is high, so that if I don't add liquid MA soon after refill then my pH remains high (in the 8.2-8.4 range). Once I add enough MA over a one week period to get TA to 50 or 60, my pH stays in the target range.

But...I don't want to add dichlor and MA at the same time as both are very acidic and I don't want my pH to crash.

Any ideas? Maybe just hold off on the dichlor and use bleach and MA until the TA and pH get in line?

 

[cowboycasey]

I would start out using Dichlor and wait a couple of hours and see what your PH is.. then you can use the MA.. you are correct not to use them together but 30 to 60 minutes between is fine..

As long as the PH is back up to 7.8 to 8 then drop it back down.. I could drop TA fast when I had mine, just run the pumps (I had 3) with air and the PH would come up fast..

It is also not hard to use bleach and drop with MA but the CYA helps buffer the chlorine..

 

[DanF]

Thanks Casey. That was my dilemma - whether it was better to get CYA (through dichlor) in the spa or lower pH with MA.

 

[cowboycasey]

CYA to buffer is better first..

 

[jseyfert3]

Dichlor doesn't drop the pH that much when the TA is high. If you are worried about pH getting too low, just test and add based on the test results and PoolMath, and you won't take the pH too low! Add dichlor, run pumps for a couple minutes to dissolve and mix, test pH. If the pH is high, add acid. With all pumps running and all jets open it only takes a couple minutes to fully mix a standalone spa. No need to wait a few hours between testing or additions. I've verified this with my Apera PH60 meter when adding acid, it's under a minute on my tub from the time I add acid to the time the pH stabilizes at the lower value, indicating full mixing of all tub water.

For what it's worth I've stopped using the dichlor then bleach method myself. That was really designed for people who already had dichlor for spas. Since I own a pool, and have straight CYA laying around for that, I just add straight CYA to my hot tub too and skip the dichlor. Poured near the filters, with the tub at temp and both pumps running on high, it dissolves in about 15-20 minutes. So now instead of adding and tracking dichlor additions over a week or so, all the CYA is in the tub right from the start. I just find it easier.

 

[Rattus Suffocatus]

I do CYA and bleach myself at a water change on my tub. Bleach and MA to maintain. I like being able to control everything individually. I have extremely high TA here and I am constantly chasing it is in both the pool and hot tub, and it's the only thing I don't control as well as I should. It's easier in the tub, though due to the much better ability to aerate... One thing you could do possibly if you don't have dogs trying to drink out of it like mine do is add some borates as a buffer, too.

 

[DanF]

Dichlor doesn't drop the pH that much when the TA is high. If you are worried about pH getting too low, just test and add based on the test results and PoolMath, and you won't take the pH too low! Add dichlor, run pumps for a couple minutes to dissolve and mix, test pH. If the pH is high, add acid. With all pumps running and all jets open it only takes a couple minutes to fully mix a standalone spa. No need to wait a few hours between testing or additions. I've verified this with my Apera PH60 meter when adding acid, it's under a minute on my tub from the time I add acid to the time the pH stabilizes at the lower value, indicating full mixing of all tub water.

Thanks @jseyfert3 - that makes sense. In PoolMath's "Effects of Adding" section I was seeing a 1.0 drop in pH when adding 2 ounces of dichlor so I didn't want to add MA on top of that. Possibly Pool Math doesn't take high TA into account when estimating pH drop in the "Effects of Adding" section.

For what it's worth I've stopped using the dichlor then bleach method myself. That was really designed for people who already had dichlor for spas.

That's me . Trying to ween through my last bit of dichlor. My issue is I have a pool also so in theory I should need CYA for the pool and the spa...except...I have about 30 pounds of trichlor tabs from my pre-TFP days that I'm trying to consume. I use those tabs to add CYA to the pool when needed during summer CYA oxidation, and in the winter when the water is too cold for the SWCG. It's good to know that CYA dissolves much quicker in a spa than in a pool; can you add CYA and MA concurrently upon refill or maybe space them out a bit due to CYA's acidity?

I do CYA and bleach myself at a water change on my tub. Bleach and MA to maintain. I like being able to control everything individually. I have extremely high TA here and I am constantly chasing it is in both the pool and hot tub, and it's the only thing I don't control as well as I should. It's easier in the tub, though due to the much better ability to aerate... One thing you could do possibly if you don't have dogs trying to drink out of it like mine do is add some borates as a buffer, too.

Thanks Fred! I'm also chasing TA but you're right it's much easier in a spa....until the next drain and refill cycle . I've been researching borates but I have a dog also so that's a showstopper IMO.

 

[jseyfert3]

Thanks @jseyfert3 - that makes sense. In PoolMath's "Effects of Adding" section I was seeing a 1.0 drop in pH when adding 2 ounces of dichlor so I didn't want to add MA on top of that. Possibly Pool Math doesn't take high TA into account when estimating pH drop in the "Effects of Adding" section.

2 oz? Are you adding that all at once because that's 25 ppm of FC in 330 gallons.

Effects of adding does not take into account current TA level. That's why there is a warning about pH calculations not being exact on that section of the app.

It's good to know that CYA dissolves much quicker in a spa than in a pool; can you add CYA and MA concurrently upon refill or maybe space them out a bit due to CYA's acidity?

I have a fill water TA of 325-400 ppm, my first order of business on a new fill is a few ppm of FC, then knocking down the TA with acid/aeration cycles. Once that's below about 100 I then start to do other stuff like CYA and salt for my SWCG.

When adding CYA I'd wait till it was dissolved and test the pH before adding MA, I wouldn't add them both at the same time.

 

[DanF]

2 oz? Are you adding that all at once because that's 25 ppm of FC in 330 gallons.

Sorry - meant to say 2 tbsps, or 1 oz. And my goal was to get FC and CYA up prior to lowering TA/pH.

 

[Rattus Suffocatus]

It's amazing how little acid it takes to make a wild pH swing with 250 gallons... I tend to add fractions of a shot glass and then re-measure pH in my tub rather that relying on Pool Math. Just not enough digits of precision in the math and precision in the measurements. In a tub, CYA is the least of your worries. You need some but it's a different ballgame than in a pool. You could probably successfully run a tub forever on 10 ppm CYA. The TA still is an issue as is going to low in pH because of the electric heating element. Acid will kill it and scale will kill it eventually.