Chlorine Levels

[BlueWave8]

PB who helped install my equipment this past weekend (Sunday) poured 2 gallons of 12.5% chlorine into my pool before I could tell him I have no CYA. Turns out it wouldn't have mattered because he doesn't fully understand what CYA is...

So...

Last night I checked and I have:

FC= 12
CC= 1.5
CYA= 0
pH= 7.35
TA= 135
CH= fading endpoint around 380-400
Borates ~50

The hardware stores that I have stopped at so far don't sell CYA, so I have some tri-chlor pucks that have been running in a feeder and I am trying to get my CYA up to around 25 or so that way.
It is an indoor pool, so I suppose it will take a while for my FC to come down, but does the CC indicate that I already need to shock again?

The Pool Calc says that 2 gallons of 12.5% would have added 16ppm FC to my pool, so from Sunday afternoon to Wednesday night it only went down about 4ppm. There was 0 chlorine in the pool when we started.

 

[JasonLion]

With plaster, having a really high FC level for a while isn't so bad.

Indoor pools are different from outdoor pools. Most of what we teach/write about is outdoor pools. In particular, it is fairly common to have CC problems in indoor pools because you don't have sunlight to help break down the CC. There is some chance that chlorine alone will break it down, but chances are you will need to use something else, like MPS, to help get rid of the CC.

 

[BlueWave8]

Thanks for the response Jason.

So this is where we were talking about MPS, UV and ozone being (possibly) useful for indoor pools. Are all of these methods equally effective? In all three of these cases the CCs are being oxidized?

Also, is my pH reading accurate at the Cl level?

 

[JasonLion]

With FC at 12, the PH reading is going to be a little higher than actual, but only a little. Your PH is on the low end of the range, but should be fine.

I don't recommend ozone for indoor pools. If any ozone gets into the air it can give you respiratory problems.

MPS and UV are both good approaches to dealing with CC indoors. UV costs money up front, but then works without much attention from you. MPS needs to be added and you also need to be aware that MPS can read as CC on the test, so when it looks like it is making things worse it isn't really. If you end up using it regularly, there is a special test reagent to neutralize the MPS so you can get a valid CC reading.

 

[BlueWave8]

Thanks again Jason.

It sounds like UV is a good fit for my situation. Would I be able to turn on a UV light only when I need to lower CCs or is it something I should leave on all the time or put on a timer? I have read that a problem with fluorescent UV units is that they are not able to put out full "rated" UV emission for very long, thus it would seem that adding a timer etc., would mean getting significantly more life out of the bulb?

If we can get a conversation started about wattages, contact time and UV light output, maybe I can start to experiment with a DIY LED UV unit?

 

[JasonLion]

It takes a quite bright UV light. I doubt that UV LEDs would work.

Most people have the UV running any time the pump is on. You might be able to optimize that with manual intervention, since the actual demand depends on how many people are swimming, but you can't improve on that with a timer that you let run without intervention.

 

[Isaac-1]

In my experience not all indoor pools are the same, a lot has to do with climate and air exchange. Mine is surrounded by about a dozen sliding glass doors which allow for ample air exchange at least in the warmer months. Also you will find that daily chlorine loss will be highly dependant upon water temperature, as water temperature goes up chlorine consumption goes up, for my pool during the middle of summer with routine, but not heavy use Chlorine demand can average up to 1 ppm per day (higher on high use days), this time of year I am seeing more like .5 ppm per day with water around 75 degrees. I tradiationally have avoided shocking using chlorine (unless there is an active algae problem, etc.) as it takes a long time to drop back down to safe swim levels, as you are currently experiencing. I only operate my pool for part of the year (extended swim season with roof top solar supplemental heat) In the past it had an electric pool heater, and I may add one again, but operation cost during the colder months was not justified by the amount of use the pool recieved, everyone seems to always be too busy to swim during the holiday season. So I generally shock with clorine at the beginning and end of the season as a preventative measure, then use MPS shock during the swim season any time the CC levels are shown to raise above .5 ppm (note as Jason mentioned there is a special test that must be used when using MPS as it shows the CC on the standard test kits). Last fall I purchased a UV Ozonator for supplimental oxidation, however I can't comment on it, as I have yet to hook it up (with a bit of luck I will have it up and going in the next couple of weeks).

Ike

 

[BlueWave8]

Thanks for the information Ike. My pool is also coming up to temperature now, so hopefully that will help get my chlorine down a bit faster. The pool room only has two single doors, and all of the windows are fixed, so air exchange may become a problem. There are some skylights that do open, but I need to purchase an extension pole to crank them open.

5 and 10W LEDs in the 365nm range are readily available (the 5W ones being significantly more affordable than the 10W ones). It shouldn't be too difficult to design an appropriate fixture. One would just have to get the contact time correct.
I have seen 40W fluorescent pool/spa fixtures that can give a dose of 30,000 uW/cm^3. I would think a similar (long life) LED fixture could be DIYed for around $300.
How capable would that amount of UV be for the supplemental oxidation needed in an indoor pool?

 

[Isaac-1]

I am not an expert on the topic of UV systems, but I did a fair amount of research before ending up buying my UV Ozonator off ebay last fall (it was new old stock and the price was right so I thought I would give it a try). The unit I have is an Ozonegenerator which uses a specific frequency of UV light to create the ozone just like ozone is generated in the upper atmosphere, Other types of ozonators work by passing high voltage electricity through the air, however these can have problems when used in humid environments. UV sanitizers operate at a different Frequency in the UV spectrum and expose the water directely to the UV light source as it passes through a clear section of pipe.

Ike

 

[BlueWave8]

Thanks for that info Ike,
So for the purpose of supplemental oxidation, what I really need to come up with is a UV ozone generator, not a UV sterilizer type device?

 

[Isaac-1]

Both types of devices can help in the reduction of CC, I suggest you research the various pros and cons to each technology. The only reason I ended up with the UV Ozonator is that I found it at a great price (80-90% off retail) as new old stock, discontinued model, etc. (the replacement model is the same basic unit, uses same bulbs, etc, just with a few bells and whistles that make installation easier, most of which I was easily able to retrofit to the older model.

Ike

 

[madwil]

The LED options should work, but don't know life expectancy and how much the output (wattage and frequency) varies with age- that's the problem with flourescents, the light output degrades over time! In fish tanks, with live plants, I used to keep- I replaced "dayglo" sunlight bulbs (13k K light ouput, i think) every 6 mths- they still came on and glowed, but the light wasn't enough for the plants...
I know "blacklights" have similar issues- light degrades over time; doing UV inspections (dye penetrant/mag part), one of the requirements is to certify the lightsource...