Proper shock technique for MasterSpa with "EcoPur" mineral stick

[dankasprick83]

Hey all,

First post here. Glad to find the group and I appreciate advice you all have. I'm writing from Lake Orion, MI. I've got a background in chemistry and lab work and I'm still finding myself having issues applying a lot of the vague information available online when it comes to the proper shock technique for one of these Master spas with the "eco pur" mineral stick (zinc and copper I believe) in addition to ozone running.

Long story short, MasterSpa for reasons that are unclear to me recommend that their spas be sanitized only with dichlor (we happen to use SpaBoss brand) and that they are shocked only with non-chlorinated MPS (we happen to use SpaBoss energize as recommended by our dealer). I'm having issues where within a week of modest dichlor usage (tablespoon every 1-2 days depending on FC readings) after a fresh fill with our city water (usually about 3 ppm FC out of the tap) we are starting to develop what looks like a chlorine lock with really high combined chlorine using our Taylor test kit. I was previously using an Oto test kit and after 4-5 weeks we tended to require more and more dichlor to keep the FC up and the water clear so I'm assuming up until I switched to the DPD kit our tub was suffering from some combination of excessive CYA and/or chlorine lock that we didn't know about.

With our current situation of one week old water and really high CC despite FC of 3 ppm I have tried twice to shock the tub as directed with our MPS non-chlorinated oxidizing shock and our readings the next day with respect to TC, CC, and FC are unchanged.

Am I barking up the wrong tree here by using this dichlor sanitizer and MPS shock routine as directed by our dealer? Is there a reason that adding the recommended amount of MPS (and then some) wouldn't be helping to convert this CC back to FC in a relatively fresh fill? Is the MPS somehow causing false readings 24h later on my Taylor test kit (I was under the impression it would have dissipated by then)?

It's a 2 year old 395 gallon tub with a relatively low bather load (small family) and I generally end up changing the water every 2 months and clean the filters frequently. I'm pretty meticulous about keeping the TA and pH within recommend ranges also.

Would love to hear anyone's thoughts on this.

Thanks all!

Dan
Master Spa LSX 850
395 Gallons with "EcoPur" mineral stick and ozonator.

 

[JoeSelf]

I'm using this as my guide. Have you read this?

How do I use Chlorine in my Spa (or pool)?

I also have ozone. It reduces CC, but also FC. I only use dichlor until I hit 30 CYA level and switch to liquid chlorine. You might have high CYA, this is what pool stores call chlorine lock. The MPS reads as CC sometimes.

 

[DrewLG]

after 4-5 weeks we tended to require more and more dichlor to keep the FC up and the water clear so I'm assuming up until I switched to the DPD kit our tub was suffering from some combination of excessive CYA and/or chlorine lock that we didn't know about.

Hi, Dan. Welcome.

How did you rule out algae or other contaminants as the reason for the increasing chlorine demand?

Is your "DPD kit" a FAS-DPD titration test where you look for a color change from pink to clear, or is it a test where you compare the color of your test solution to a reference?

How are you determining CYA concentration?

Is there a reason that adding the recommended amount of MPS (and then some) wouldn't be helping to convert this CC back to FC

You've got the chemistry background, I don't. But as I understand it, MPS oxidizes organic material so chlorine doesn't have to, PREVENTING the formation of CC -- but it doesn't eliminate CC that's already present or convert CC to FC.

Is the MPS somehow causing false readings 24h later on my Taylor test kit (I was under the impression it would have dissipated by then)?

It takes two days for MPS to dissipate in my pool, and my dosage is probably only a quarter of yours (I use 16 oz for 8000 gallons). You could rule out MPS interference in the chlorine test with Taylor's K-2042 kit (link is in my signature).

 

[dankasprick83]

Thanks all. I am currently not testing for CYA. I will get another Taylor test kit that includes those reagents.

I will also review the dichlor/bleach protocol. Thanks for providing link.

As far as testing kit goes, it is a Taylor DPD test kid where I am matching the color rather than watching for a color change. Do you advise that I switch to another kit?

Drew, maybe I'm showing my ignorance with this answer but I'd say the only reason I've ruled out algae or other contaminants is that we've always had a relatively low bather load and we don't even really build up any scum around the surface (like never). I used one of the purge products recently in order to potentially clean anything out that was present in the pipes (not sure if those are legit or not) and there really wasn't much material that seemed to wash out. Is there a more definitive way that I should be ruling out these other contaminants?

Thanks for the comments all,

Dan

 

[DrewLG]

I am currently not testing for CYA. I will get another Taylor test kit that includes those reagents.

Good. I think you need to get your own test, if you suspect that excessive CYA may be an issue in your hot tub. Pool-store CYA testing is apparently very inaccurate.

As far as testing kit goes, it is a Taylor DPD test kid where I am matching the color rather than watching for a color change. Do you advise that I switch to another kit?

First, I know a little about pools and nothing about hot tubs. So any or all of my advice might be inappropriate (and if so, I hope one of our resident hot tub experts will correct me).

That said, the FAS-DPD test -- which is available from TFTestkits for $32 or from Taylor with less reagent for $41 -- is more precise, easier to read, and can measure across a much wider range of concentrations than the color-comparator tests. The directions from TFTestkits show how to get 0.5ppm/drop resolution, but for finer measurements there's a simple modification (25ml sample instead of 10ml, two dippers of powder instead of 1) that makes each drop of the titrating reagent worth 0.2ppm instead, which might be better for a hot tub.

If you want to go all in with a kit that also measures CYA, pH, Total Alkalinity, and Calcium Hardness, look at the Taylor 2006-C or TFTestkits TF-100 or TF-Pro (which use Taylor reagents, but in quantities more tailored [haha] to residential pool-owner needs). Those are the only complete kits that are ever really recommended here.

I'd say the only reason I've ruled out algae or other contaminants is that we've always had a relatively low bather load and we don't even really build up any scum around the surface (like never). I used one of the purge products recently in order to potentially clean anything out that was present in the pipes (not sure if those are legit or not) and there really wasn't much material that seemed to wash out. Is there a more definitive way that I should be ruling out these other contaminants?

If it were a pool, there's an easy way called the Overnight Chlorine Loss Test, or OCLT: Raise the FC level to somewhere in the typical range for water with CYA (like 5 to 10 ppm), measure FC at night after the sun sets, then measure again in the morning before the sun rises (the test is performed overnight to eliminate any FC loss due to UV from the sun). If more than 1ppm FC was lost overnight, algae or other organic contaminants are present and using up your chlorine.

But with a hot tub, I don't know whether 1ppm is a reasonable threshold. And I've heard that at least some hot tub owners want only a minuscule concentration of chlorine in their water; they probably wouldn't be willing to raise FC to a measurable level, so I don't even know whether OCLT is an appropriate test for hot tubs.

Again, I hope someone more expert will chime in.

FWIW, the "Ahh-Some" hot tub purge product has been extensively reviewed here, very favorably.