First set of readings with new TF Test Kit...help please?

[chriszke]

We've been testing with guess strips for a little more than a year. We've got a pool store with a pretty solid neighborhood reputation that we take water samples to about every other week. They do pH and chlorine readings, but very little else unless we've got a visual problem.

My wife usually tends to the pool chemistry, but I've offered to that that job and purchased the TF Test kit to help.

We had a small bout with algea about 10 days ago, but raised the chlorine level, did some brushing and vacuuming and feel like we are about back to normal.

I ran a set of tests on this past Wednesday...then another today...just to practice with the kit & get a feel for pool chemistry rates of change.

Anyways...here's the data:

Weds....................Fri
--------................-----
FC: 19...............FC: 17
CC: 1...............CC: 0
TC: 20...............TC: 17
pH: 6.8..............pH: 7.2
T/A: 100............T/A: 110
CH: 220.............CH: 220
CYA: 90..............CYA: 90

It's a 24' round pool with a 4' depth. About 13,500 gallons I believe. Sand filter.

We keep a floating pool chlorinator & add a pre-dissolved 1lb package of powdered shock routinely once or twice a week (depending on usage, weather, guess strip readings & feedback from the pool store).

After seeing Wednesday's test results & noting the low pH level, I consulted the poolcalculator (erroneously inputting 12,000 gals), which suggested about 75 oz of Borax to raise the pH. I bought a box & broadcast the whole thing (about 77 oz) into the pool wednesday evening. Our filter runs 7 hours during the day, and another 7 hours while we sleep.

Anyways, the pH moved from 6.8 to 7.2, which was less than I had targeted...but then, I failed to account for about 1500 extra gallons of water. I'll add more Borax this evening & try to fine-tune the pH to 7.5.

My free chlorine remains high, but did fall 2 ppm in 2 days. I'm a tempted to take the floating chlorinator out to allow the chlorine level to fall faster, but because we'll be away for the long weekend, and fresh from a battle with the algae-monster, I'll probably keep it in and let the FC fall slowly.

My wife will want to add another pound of powdered shock before we leave for the weekend (she HATES algae) , but I don't see the need, especially if the pool remains covered and the floating chlorinator remains in.

Anyone see anything else that looks odd or out-of-whack?

Am I sound in my reasoning to resist adding additional powdered-shock chlorine for the weekend, given the Friday morning readings?

 

[duraleigh]

Some random thoughts in response:

I would leave the pH alone @ 7.2....that's a very nice number for now...no reason to change it

I would recommend getting rid of the floating chlorinator after this trip.....it's adding CYA to your pool and you're already too high. (also, it's contributing somewhat to your low pH...with the floater gone, your pH will most likely do a slow rise)

I would also suggest only shocking when your test results or water clarity demonstrates the need and, then, I would shock only with liquid chlorine.....that powdered stuff is likely adding CYA as well and you absolutely don't need a bit more.....30-50ppm would be much better than your results of 90ppm

The rest of your test results look quite good....I wouldn't change anything except to have a fire sale on the powdered shock and save that floating chlorinator for when you're out of town.

PS - your method of practicing first with the kit is really a good idea. I tested my tap water and my pond water a couple of times before my pool was filled.

 

[chriszke]

Thanks for the comments Dave.

No need for a fire-sale on powered chlorine...we've been going bag-to-bag while the season runs out. We'll stay on liquid for the balance of the season and stay on the liquid diet hence-forth.

Got very few of the floater-pucks left as well, we'll save those for vacations and long weekends.

I was a chemistry major two or three decades ago. While I change from Chemistry to Engineering, I've enjoyed doing the drop-tests and recording of data.

Thanks for the look and the comments.

Chris

 

[chriszke]

Help me figure something out please.

I've posted my initial testing results. (see above)

Just prior to the labor day weekend, I re-tested the pool. FC had fallen from 19 to 17 ppm, with zero CC.

Because we were going away for the weekend, I put three chlorine tabs in our floater, placed it in the center of the pool and replaced the solar cover on the pool. We would be gone from Friday to mid-day Monday (gone about 72 hours). Our filter was on a timer, running 7 hours during mid-day, and 7 hours again overnight.

When we arrived home, we removed the solar cover and saw light patches of green algae beginning to form on our vinyl liner walls. We brushed the walls and ran the filter 24 hours. I ran the Kreepy Krawly at night to scour the pool bottom (and walls) and we were good by morning.

I understand that my CYA level (at 90) is high, and that I need to maintain a higher FC ppm to effectively combat algae.

With pool closing just a couple of weeks away, it seems silly to remove and replace water this season to drop the CYA. (we'll be removing water during the closing).

Anyways....at CYA=90, isn't FC at 17 to 19 enough to keep the algae away? I'm wondering whether keeping the solar cover on...and the lack of water agitation (by swimming) was contributing to alrea growth?

Any ideas?

 

[JasonLion]

That is curious. With CYA of 90, FC of 7 or higher should be enough to keep algae away except in rare cases. FC of 17 should be more than enough in all cases. The only thing I can think of is possible bad circulation. Your results wouldn't surprise me if you had left the pump off. If your circulation pattern is particuarly bad that could explain it, but normally 14 hours of pump run time a day is enough even with a fairly bad circulation pattern. Is there any possibility that the pump wasn't actually running while you were gone?

One other thought. High PH can reduce the effect of chlorine. If you PH was above 7.8 that could begin to explain things.

 

[chriszke]

Jason,

Thanks for the response.

There is no chance that the pump didn't run, as it was on a timer which still cycled correctly upon our return. The weather was beautiful in Michigan this weekend...so power interuptions were unlikely.

The pool is 24' round and has just the single inlet. I had disconnected it from my solar heaters (which robs the flow-rate)...so flow wasn't an issue...but I was speculating whether water direction might be...

I've currently got the inlet eye pointed towards the bottom of the center of the pool. I was wondering whether aiming it off-center (and creating more water movement around the perimeter) might be a good thing to try.

Our pH has been pretty stable at 7.2.

 

[JasonLion]

Down and to one side is better, but with a round pool down and straight across isn't so bad.

Even more of a mystery.

 

[chriszke]

Of all of the tests in the kit...that CYA test looks to be the most difficult to learn and interpret.

As I read in another thread...as you go up the scale in the CYA test...you lose a certain degree of accuracy. I'm wondering if I've got REALLY good eyes and perhaps my CYA levels are actually higher than 90.

Jason...you seem to have a pretty good feel for the CYA-FC relationship.

Given a FC level of say...17, how high do you suppose the CYA would have to be before I lose Algae fighting capability?

Also...lets say 90 is a true number. Given a pool closing in a couple of weeks...would it be a good idea to drain off say...a couple of feet of water (targetting a next-spring CYA level of 45) then adding water to get up to our below-the-skimmer winterized level?

Somewhere on this forum I read about bacteria eating CYA over the winter...but I doubt I can count on that to get my levels down where I'd like.

 

[JasonLion]

If you never let the FC go below 17 and the PH stays reasonable then you would usually be able to keep the algae away up to a CYA level of 170 or perhaps even 200. Of course that is not something I recommend trying if you can possibly help it.

The CYA test is rather subjective. Plus levels over 100 will often read as 100, which you could be reading as 90. One double check you can do is to dilute some pool water one to one with tap water, do the CYA test with that, and then multiply the result by two. The result will be significantly less percise but it will tell you if your CYA is really somewhere around 100 or actually much higher.

Not every pool has the CYA go down over the winter. If you want to raise the odds of CYA going down over the winter leave a number of leaves in the pool and don't add any extra chlorine or algecide. There is still some chance you won't lose all your CYA over the winter and the pool is sure to be a mess come spring, so that might not be worth it for you.

If you are close to closing anyway I would go ahead and close normally and then find out what the CYA level is in the spring before going to any extra effort to replace water right now. Where I am, and using a pool heater, we can hope for six to eight more weeks of swimming. In which case I would do some water replacement now and then more later over the winter.