Combined Chlorine Help

[frito]

Hi there -- new to the forum but have learned a tremendous amount already (thank you!). I need some help with my CC levels in my hot tub.

360gal Hot Tub 100 degrees using Chlorine (Sodium dichloro-s-triazinetrione hydrated to be specific).

I've read the "How do I use chlorine" post and learned a lot, but I feel like I'm still missing something.

pH: 7.4
TA: 50
FC: Was 1ppm, added Dichlor to raise to 5ppm

My trouble is with CC. I have been adding (what I thought was) the recommended amount of non-chlorinating shock once a week or so after using a few times per week. I know that MPS can register as CC, but how long does that continue to show up? When I do the test with my Taylor K-2006 (using 10ml of water), I'm adding something like 40 drops of R-0871 to get the pink color to go away after adding the 5 drops of R-003. The hot tub does have a slight chlorine smell when I remove the cover, but it's not overwhelming and I don't feel itchy or stinging when it's in use.

I'm either so far out of the ballpark and my CC levels are truly 20ppm or the MPS is throwing me for a loop. I suspect the latter, but wouldn't be surprised by the former. Is the R-0867 that helps with the MPS showing in CC levels worth it or am I just going crazy?

 

[Mdragger88]

It may be both-
High cc’s & mps interference.
You can purchase the Taylor interference reagents to remove that confusion if you wish to keep using mps.
You’re missing a key parameter- cya.
The amount of fc needed to keep the tub sanitary is based on the cya level.
See —> FC/CYA Levels
1ppm fc is too low for virtually any amount of cya and if you have been regularly using dichlor your cya may be very high making keeping the tub sanitary harder and harder.
For Each 1ppm of fc dichlor adds it also adds about 1ppm of cya if your dichlor is 99%.
It becomes quite difficult & impractical to maintain a tub with cya higher than about 50ppm.
If you’re chronically under sanitized you will likely have higher than acceptable cc’s.

 

[frito]

I think my CYA is around 20 or less. The test kit I have doesn’t kick in until 30 so I know it’s at least below that.

Is the best course of action to continue to maintain FC levels at the higher end of the 3-6 range and no more MPS shock? When CYA is at 30 switch to bleach as recommended?

 

[wireform]

How old is the water, last purge?

 

[frito]

How old is the water, last purge?

Water is new as of September. Planning a drain/refill at the start of the new year.

 

[wireform]

The recommended product here for the purge is Hot Tub/Jetted Bath Plumbing & Jet Cleaner (2 oz.)

 

[Mdragger88]

In that case, if you believe your cya test is accurate, I would just discontinue mps & be sure you’re dosing high enough to stay above min for your cya at all times. You may want to bring it to shock level a couple times to combat any actual cc that you have & see if the number falls.
You can use
PoolMath effects of adding to try to estimate how much dichlor you have added & how much cya that comes out to.
Even with no cya the minimum fc should ever be is 2ppm.
Mps is only an oxidizer.
Chlorine is both an oxidizer & a sanitizer. Easier to just stick with chlorine.
Its kinda hard to believe that you’ve been dosing with dichlor since September & have no cya though.

 

[frito]

The recommended product here for the purge is Hot Tub/Jetted Bath Plumbing & Jet Cleaner (2 oz.)

Thank you! When I drain and refill I will get some of that.

In that case, if you believe your cya test is accurate, I would just discontinue mps & be sure you’re dosing high enough to stay above min for your cya at all times. You may want to bring it to shock level a couple times to combat any actual cc that you have & see if the number falls.
You can use
PoolMath effects of adding to try to estimate how much dichlor you have added & how much cya that comes out to.
Even with no cya the minimum fc should ever be is 2ppm.
Mps is only an oxidizer.
Chlorine is both an oxidizer & a sanitizer. Easier to just stick with chlorine.
It’s kinda hard to believe that you’ve been dosing with dichlor since September & have no cya though.

Thank you so much for your reply, I really appreciate it.

I haven’t been adding regularly due to somewhat infrequent use and, honestly, lack of really knowing what I was doing. Probably only a few caps of it over the course of a month or so. I do have one of those floating Frog things and my tub never looked green or cloudy so I assumed I was okay. One of those “if it ain’t broke” ideas.

 

[Mdragger88]

Thank you! When I drain and refill I will get some of that.

Thank you so much for your reply, I really appreciate it.

I haven’t been adding regularly due to somewhat infrequent use and, honestly, lack of really knowing what I was doing. Probably only a few caps of it over the course of a month or so. I do have one of those floating Frog things and my tub never looked green or cloudy so I assumed I was okay. One of those “if it ain’t broke” ideas.

Well, that explains it! The frog shows up as cc’s too!
Best advice is to ditch the frog & just follow the dichlor then bleach method as outlined in the guide.
Clear doesn’t automatically = sanitary.
Accurately Measuring & monitoring cc’s is crucial part of judging the health of the water in a hot tub so you really need to be able to do that. Persistently elevated cc’s mean its time to purge then refill.