Totally confused regarding weekly pool service.

[jblizzle]

maybe. Have you asked them what they are doing?

 

[harleysilo]

If I were you I would tell them I had some relatives coming and they are really opposed to a chlorine pool, something about how they have a natural pool or some nonsense, and then I would ask them to explaind what the do and use under the guise that you can assure your relative everything will be okay....

 

[chem geek]

My test result from the later in the day after he serviced the pool.

FC 10
PH 8.2
Alkalinity 70
CH 350
CYA 50

It seems a bit out of wack and CYA went up roughly 10.

:

We do have a net cage over the pool that supposedly blocks a percentage of UV and we hardly ever get debris in our pool as a result. The pool also gets very minimal usage as kids are gone and we have no pets. Might get moderate usage 1 or 2 weeks a year when family visits.

I am still confused by how the CYA level is not completely through the roof or could it be the liquid and granular chlorine used this week were both unstabilized meaning he is using pucks to get it to a desired level then switching to granular and liquid unstabilized?

If this is the case is there any chance the FC levels could last until next weeks service without algae starting to appear?

Is it possible algae is starting to grow before service but is not visible and he eliminates it with the liquid shock?

You had mentioned before that you noticed tabs in your skimmer so they may be adding that every now and then and perhaps calling that "stabilizer" even though it's Trichlor which is a chemical combination of chlorine and stabilizer.

I forgot that you had talked about the pool being in a "cage" so partially shielded from sunlight. That will make a big difference. It does sound like he's raising the FC to 10 ppm and that it drops down into the 3-4 range which with your CYA is marginal, but OK since he then comes again and raises the FC to 10 ppm. He might have used other products at the start of the season (e.g. phosphate remover) as insurance against algae to at least slow it down if the FC got too low.

He added chlorinating liquid which had the pH go up and it should drop down as the chlorine gets used/consumed, but I'm a bit surprised that he didn't add enough acid to start with no higher than 8.0 for pH. If you had metals in the water, then your pool surfaces could get metal stains at that high pH. As for the powder, it's most likely to have been Cal-Hypo since it's pricing is somewhat comparable to Trichlor and chlorinating liquid (ignoring pH adjustment chemicals which he is probably not considering). Dichlor is more expensive and lithium hypochlorite is very expensive.

The CYA test is +/- 15 so a change in 10 may not be real and could be test variation. It's a hard test to nail perfectly anyway.

If you are able to test the chlorine level just before he visits, that would be great info to know. I redid the table below for the 25% daily loss and a lower 15% daily loss, but this time these do not have any Trichlor being added.


............. 25% Daily FC Loss ..... 15% Daily FC Loss
Day 0 ... 10 ppm FC .................. 10 ppm FC
Day 1 ... 10.0 * 0.75 = 7.50 ...... 10.0 * 0.85 = 8.50
Day 2 ... 7.50 * 0.75 = 5.63 ...... 8.50 * 0.85 = 7.23
Day 3 ... 5.63 * 0.75 = 4.22 ...... 7.23 * 0.85 = 6.14
Day 4 ... 4.22 * 0.75 = 3.16 ...... 6.14 * 0.85 = 5.22
Day 5 ... 3.16 * 0.75 = 2.37 ...... 5.22 * 0.85 = 4.44
Day 6 ... 2.37 * 0.75 = 1.78 ...... 4.44 * 0.85 = 3.77
Day 7 ... 1.78 * 0.75 = 1.33 ...... 3.77 * 0.85 = 3.21

So again you can see that your daily chlorine loss rate is key (and this time I show the last day 7 which starts the next week).

 

[Steve2968]

Funny you should mention stains on the surface. I have brown stains on the pool floor and stairs that look like small patches of rust.

We did mention it and he told us he would look into what to do to get them removed.

 

[chem geek]

Sounds like iron stains. Ascorbic acid (Vitamin C) will remove those (technically redissolving them into soluble form in the water). There might not be that much metal in the water if you didn't have staining before the pH rose, but a metal sequestrant would keep a removed stain in the water and prevent it from being redeposited, but a metal sequestrant will have to be regularly added as it gets broken down by chlorine. It will be interesting to see what the service guy does.