I screwed up with MPS

[presse55]

A couple of days ago, I noticed that the 20 day old water in the spa had lost a bit of it's sparkle. The FC, pH and other parameters have been OK since the refill; still, for good or bad, I decided to treat with MPS.

I should have put in 30g (6 tsps), but wasn't careful enough and ended up putting twice as much , 60g (12 tsps).

Here we are two days later and the FAS-DPD test shows FC at 17 ppm; pH 7.6.

Now the water is clear, and the other parameters as in my signature.

So my questions are:

• Is the water safe to soak in?
• Is the pH reading reliable?
  I have read that at FC levels 10ppm or above, the Taylor pH test is unreliable.
• How can I monitor the 'true' FC level, while the MPS throws the reading off?

Note: I've left the SWCG run unchanged, so the usual chlorine quantity is being generated.

Regards,

Ron

 

[JoyfulNoise]

The MPS will show up as excess FC on the DPD-FAS titration test. The only way to account for it is to buy the Taylor MPS interference removal reagent (Taylor K-2041). However, MPS should get used up within 48 hours or so and no longer register.

As for advice on soaking, you will need to provide a full set of test results including CYA level as that is critical in knowing if your water is safe to soak in.

 

[presse55]

Thank-you Matt.

My results are as follows:

FC: 17 ppm;
CC: < 0.5 ppm when last measured 3 days ago;
pH: 7.6;
CYA: 25ppm;
AT: 45ppm;
CH: 125ppm;
Borates: 40ppm;
Salt: 1000 ppm = mfg. specs;

Many thanks!

 

[JoyfulNoise]

I just saw your parameters in your signature. I realize that they probably don't change much, but it is preferred to post your results and not put them in the signature. Most of the mods and guides here won't look there for data and, anyone using a mobile app like Tapatalk, will likely not see them at all.

Any FC above 10ppm with a CYA at or near 25ppm will be at an FC/CYA ratio of 40%. That is what TFP considers shock level FC. While it is generally ok to swim in a swimming pool all the way up to shock levels, I can't say for sure that it is ok to do so in a hot spa where excessive FC is likely to create a lot of THM and DBP compounds. That can easily lead to making someone feel sick. I would suggest you wait until your FC returns to normal levels and then soak. If you can't wait that long, small quantities of hydrogen peroxide can be added to lower the FC chemically. But please note that peroxide additions will react with FC and cause the pH to drop so you need to monitor pH carefully to ensure that you do not crash the TA that is in your tub.

If I were in your situation, I would wait.

 

[presse55]

Makes perfect sense, Matt.
We'll hold off on soaking then, and won't bother with the H2O2.
Thanks

Ron