Chlorine level rising

[gregch]

First off, at the risk (certainty!) of incurring the wrath of the TFP, my pool is dosed with chlorine pucks rather than liquid chlorine or SWG or whatever - it's just how it's done here in Europe - particularly in older pools - and haven't generally had any issues.

For the first time in a while I'm having trouble with the water. Everything was fine, and consistent, earlier in the season, and I was maintaining FC at about 3.0 and TC 0.1 or 0.2 higher. Over the latter part of the season, I noticed chlorine levels were rising each time I tested, even though the chlorine dose was the same - and pH and TA and CyA all pretty consistent (and where they should be).

When I saw that FC had risen to 5.0, I stopped dosing any chlorine. Now, 3 or 4 days later, without adding any chlorine to the pool, FC is at 5.5 (TC is only 0.2 higher)!

The full test results as of just now are:
FC 5.5
TC 5.7
pH 7.5
TA 98
CyA 47

We're in the UK, and it's been a terrible summer, so not a whole lot of warmth or sunshine (and so not too many days in the pool), haven't had the friends' kids over as in previous years, and have had the solar cover over it much more than usual. Would that account for it?

Only other thing I can think of is that about the time this happened I'd started using cheapo no-name chlorine pucks in place of the usual brand; but have been back to using the regular hth brand now for a while, and it hasn't made a difference.

Any ideas? Doesn't look like we'll be getting much more of a swimming season anyway this year so I guess it'll get drained down anyway soon enough but I don't like not being able to figure stuff out and know what's going on!

 

[Bperry]

Depends on how you’re testing the water. The test strips and some of the electronic gizmos aren’t known to be super reliable so we don’t trust them. Since they can lead to strange problems like: “I haven’t added any chlorine but my chlorine level keeps rising.”

I get you folks over there can be kinda limited in test kit availability so sometimes you do the best with what you can.

 

[gregch]

Exactly that! I'm using a Lovibond photometer tester and I'm not sure I would trust it 100% but it is pretty consistent (eg testing again with a fresh sample gives the same results, etc) and more accurate than test strips. I've been using it for 2 or 3 years now (with fresh test tablets each season) and it's seemed to give OK results. I've tried repeatedly to find the Taylor kits or equivalents here but proved impossible - occasionally they're listed on Amazon but often with out of date test liquids, which are in any case hard to replace here.

I did wonder about getting hold of an alternative test kit of some kind, so as to get a second opinion. I'd like to try and avoid going to a 'pool guy' as my past experience with them hasn't been great.

 

[Bperry]

Exactly that! I'm using a Lovibond photometer tester and I'm not sure I would trust it 100% but it is pretty consistent (eg testing again with a fresh sample gives the same results, etc) and more accurate than test strips. I've been using it for 2 or 3 years now (with fresh test tablets each season) and it's seemed to give OK results. I've tried repeatedly to find the Taylor kits or equivalents here but proved impossible - occasionally they're listed on Amazon but often with out of date test liquids, which are in any case hard to replace here.

I did wonder about getting hold of an alternative test kit of some kind, so as to get a second opinion. I'd like to try and avoid going to a 'pool guy' as my past experience with them hasn't been great.

A FC of 5.5 with CYA of 50ppm is totally normal and fine to swim. But cooler weather and less sun tends to consume less FC.

 

[gregch]

That's reassuring, appreciated.

 

[reggiehammond]

FC/CYA Levels - this is the whole basis of TFP methodology.
FC is safe for swimming up to SLAM levels, but below minimum FC, algae can take over.

 

[gregch]

Reassuring, but something's still a bit weird... FC fallen to 5.4 from 5.5 after another two days; so no chlorine added at all for a week and there's been pretty much no chlorine loss. In fact it's still higher than when I stopped dosing chlorine a week ago. Admittedly, the weather here this summer has been beyond terrible, high today barely 66 deg and hasn't stopped raining. I've also ordered another test kit so I can sense-check the results. Has anyone come across this before (absolutely no loss of chlorine for a week or so)?

 

[mknauss]

I believe you pool is indoors (please add that to your signature) and if cloudy and raining all week, no organics blown into the pool, and no swimming, it is very possible to have limited FC loss. There is error in your test methods, so that may account for some variation.

 

[cwswifty]

FC fallen to 5.4 from 5.5 after another two days;

I do not believe it is possible for your measurement equipment to accurately measure down to 0.1 resolution. What kind of test kit are you able to get in the UK? Either one of these available?
Test Kits Compared

 

[gregch]

I do not believe it is possible for your measurement equipment to accurately measure down to 0.1 resolution. What kind of test kit are you able to get in the UK? Either one of these available?
Test Kits Compared

You're almost certainly correct. This is using a Lovibond Scuba, a cheap photometer. Unfortunately, none of those test kits is available in the UK. I found one of the Taylor kits on Amazon that would ship to the UK, but the reagents were specified as being almost out of date, and it wasn't possible to source those in the UK.

So that's not ideal, but I guess what I'm saying is it's still up around 5.5 ppm, ie hasn't changed, despite having stopped all chlorine dosing a week ago.

The pool is an outdoor, in-ground pool; though it has certainly been cloudy and/or raining, and pretty cold, throughout that time. The results from the Scuba thing have previously matched expectation, at least, but I do wonder know if it's gone a bit flaky. I'll try and get a hold of an alternative as a sense check.

Thanks for everyone's wisdom, as ever, much appreciated!

 

[mknauss]

The pool is an outdoor, in-ground pool;

Is it covered? I would think it would be a big challenge to keep the water warm enough to swim in with an uncovered, outdoor pool in UK.

 

[gregch]

Is it covered? I would think it would be a big challenge to keep the water warm enough to swim in with an uncovered, outdoor pool in UK.

It is, yes, there's a bubble-type cover (which is surprisingly effective at not only keeping heat in but also using solar heat gain to warm it up a bit). In a typical UK summer, we can maintain it through the season at about 24-26 deg C (75-79 F) without heating. So it's not warm, exactly, but perfectly fine for swimming in on a warm day!

One of these days I'll get it heated again - I'd planned to put in a new heat pump as part of last year's refurb but ran out of time and budget as other stuff got in the way.

It is, in my opinion, debatable as to whether the UK's a suitable place for an outdoor pool but it was here when we bought the place, and several of our neighbours also have one. On the rare occasions we get a good summer, or a run of hot days, it sort of seems to make sense though!