What is this film on our water?

[TroubleFreePat]

Lately, when I open the pool (We have an auto-cover we keep on unless we're using the pool), I notice this "film" on the top of the water. It disappears quickly once the cover is opened and my thought is that it's simply "stagnant" water that is in contact with the cover at the surface. Since the cover is on, the top of the water just sits? No idea, but again - it clears in maybe 10-30 minutes with the filter running.

Thoughts? Not sure I ever had this before the cover, but we also got the cover late in the season, and this is our first year with the pool, so. . .

Latest chemistry below. Yes, FC is very low. Still trying to get the hang of setting the SWG properly with the cover. I also use the BBB method.

Also wondering if this has anything to do with the "scum" on the side of the pool ABOVE the water line. I can't even really call it scum. It's just a white film that does come off with some liberal Magic Eraser cleaning. Was going to do the vitamin C test, but haven't gotten to the store yet. The water fill was about 60% from a truck, and 40% from municpal water.

pH: 7.3-7.4
Borate: 50
FC: 1.5
CC: 0
TA: 80
CH: 220
CYA: 70
Water temp: 67*

Chemistry has been VERY stable (With the exception of the FC being low.) This is the first the pH has gotten this low and has been around 7.5 all season.

Last comment - whenever I test my water (TFT), when I do the CH testing, I always add five drops of the reagent first as I noticed the test "globs." I get a good result and use a speed stir, but still notice this when testing. So maybe it does have to do with metal?

See pictures. Thanks!

 

[linen]

Chemistry has been VERY stable (With the exception of the FC being low.)

This is a problem!

At 70 ppm cya, you never want the FC to below 3 ppm. Since you have let it drop low, you may have algae in the pool. I would do an OCLT with your FC up around 10 ppm to see if you need to do the SLAM process: http://www.troublefreepool.com/pool-school/overnight_fc_test

It is very likely if you get rid of the organics in your pool and keep your FC up above the minimum, the film may be gone.

 

[Patrick_B]

I'm not sure about the film on the water surface, but the scum above the water line is likely just minerals deposited from the pool water. The clumps or grains you see in the CH test photo is precipitated mineral. No need for concern with that.

What is concerning is your very low FC level. If you don't get this up within guidelines of the CYA/Chlorine chart you are headed for a green pool as well.

 

[TroubleFreePat]

OK, before we get too crazy, let me just add that FC is only low this week. I turned it down as last week it was around 20. Temps dropped here pretty quick and the pool has been unused for quite a while, so since it's been basically closed (With the auto cover), the SWG has been too high. I turned the SWG off and it took about two weeks to get to a normal level (I keep it around 6 normally.) I fired it back up but set it too low. Bumped it higher today, so we'll see if that's enough to swing it in the right direction.

Regardless, I'll check out the OCLT so we can all sleep easily!

Any ideas on the film though? This began even when the FC was high.

 

[TroubleFreePat]

OK, so this is my first time doing an OCLT.

Make sure I'm thinking this through correctly. Normally, my pump/SWG runs from around 11am to 5pm. I'm going to let it run and finish today's cycle just to get the FC up a bit. Once 5pm hits, it shuts down and I'll leave it alone. Tonight, after sun down, do a drop-test. I'll cover the pool as I normally do. Then do another drop-test first thing in the am, which will be before the SWG comes online.

Good?

EDIT: I see now you're recommending getting FC around 10 to do the test. So I definitely want the SWG running today. I'll crank it up a bit more to move the FC in faster.

Thanks!

 

[TroubleFreePat]

One more picture - now that the condensation on the side of the pool has burned off with the cover open, you can see more of what I mean. It wasn't until recently that you could see a real line around the pool. I'm thinking I might have two issues going on here. Guess we'll find out in the AM.

 

[linen]

EDIT: I see now you're recommending getting FC around 10 to do the test. So I definitely want the SWG running today. I'll crank it up a bit more to move the FC in faster.

I would just use bleach/liquid chlorine to raise it up from where ever it is at 5 pm to the 10 ppm level after the sun goes down. Make sure you give the chlorine an hour to mix before doing your evening test and leave the pump on all night.

I'm thinking I might have two issues going on here. Guess we'll find out in the AM.

Possible, though the film could also be a result of the low FC.

 

[jblizzle]

To confirm, you want the pump running all night. So you will have to turn off the SWG separately.

 

[TroubleFreePat]

To confirm, you want the pump running all night. So you will have to turn off the SWG separately.

Because of the chlorine, or is that a requirement of the OCLT?

 

[jblizzle]

You want the pump on for the OCLT ... to continually be circulating the water.

 

[TroubleFreePat]

Roger that. May want to include that in the pool school inf on the OCLT. I didn't see it on that page, but I may have missed it (Checked twice.)

 

[jblizzle]

Roger that. May want to include that in the pool school inf on the OCLT. I didn't see it on that page, but I may have missed it (Checked twice.)

Good point, it is not
Likely because normally someone would be in the SLAM process which says to leave your pump on.

 

[Patrick_B]

To confirm, you want the pump running all night. So you will have to turn off the SWG separately.

Because of the chlorine, or is that a requirement of the OCLT?

It is because when you perform an OCLT you do not want to be adding more FC during the process. You are trying to see how much is being lost, and doing it at night removes the loss to sunlight factor.

If the SWG is making more FC, it skews the loss result. Hopefully that makes sense...it's still early in the day for me.

 

[TroubleFreePat]

Yes, definitely got the point that we don't want the SWG running overnight to skew the test. Just wasn't clear on the pump.

So. . . I didn't get FC up to 10 yesterday. 3.5 is what I got. I checked it again first thing this morning and it didn't move a bit. So that's a good sign. I assume we want it up to around 10 to see if there's any minor variations (Well, minor above 1.) So I'll try it again tonight after leaving the SWG on all day. But so far so good, I think I'm in the clear.

 

[TroubleFreePat]

So I didn't get a chance to get to the store and get bleach yesterday. I did leave the SWG at 100% all day (8am-5pm) so that helped. Last night before bed, I was up to 8.5 for FC. This morning I was down to 8.0 for FC. So we're still within acceptable range for the test. CC is still 0. And we still have a "film" on the water.

Any other thoughts?

 

[nikon5400]

3 years ago my water looked like the water in the test-tube when calcium was tested. my calcium was around 700 at that time. Don't know if it looks like that now, my calcium is 200-300, so I stopped testing it