FC Dropping MUCH Faster Than Usual

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Petebacher

Petebacher

0
Bronze Supporter
Jun 19, 2017
22
Kennett Square, PA
Greetings All -

First year managing my (new to me) 30k+ gal in-ground pool using TFP. All has been good since an early-season SLAM. Lots of rain this season, so I've been able to lower my CYA from 90 earlier in the season to the high 40s recently. I'm using liquid shock to chlorinate - my daily target is 11, with typical overnight FC drop to 8 or 7. Until about a week ago.

Suddenly I'm lucky if FC is over 4 each night when I test. Most nights it's now right AT 4 every night. So I dump in 3 gallons of shock, taking it to 13 or so, and next evening I'm back around 4.

Anyone have any ideas what might be causing the sudden rapid FC loss? I am seeing no change in water clarity (it's crystal clear), and no change in filter pressure (when I had an algae bloom and cloudy water earlier in the season, I saw a very telltale rapid rise in filter pressure). The only incident I can think of is that about a week ago we had a storm that dumped a bunch of leaves into the pool, and I wasn't able to get them out until two days later.

Thanks!

-Pete
 
Pete,

Your pool should not loose more than 1 ppm of FC overnight... If it does it means you have something in your water consuming your chlorine.

You need to run an Overnight Chlorine Loss Test.. (OCLT). See how... Overnight Chlorine Loss Test The hardest part is getting your rear out of bed before sunrise... :cool:

If you fail the OCLT, you will need to perform a full SLAM... See this... SLAM Process

Thanks,

Jim R.
 
Pete,

The lower the CYA, the faster the sun will consume your FC. And the higher the FC is over the recommended amount in this chart... [FC/CYA][/FC/CYA] then the faster the excess will burn off.

With that said, it seems something is not right. I'd still do the OCLT, just to make sure..

Thanks,

Jim R.
 
Thanks again Jim -

I agree with your assessment - the only LOGICAL thing I can think of (though I have very little experience - only my reading here and a scientific mind) is that FC should drop more than 1 point overnight.

That said, I just measured FC and it was where it should be... sort of. When I chlorinated last night the pump had already turned off - it was off this morning as well. I disperse the liquid shock as best I can by pouring it in as I walk around the pool, plus a bit more at the deep end. This morning I took 4 measurements. 23, 24, 29, 29 at various points around the pool. A bit more widely spaced than I would have preferred, but the average of 13 was right where it should be (13.5 would have been 0 FC loss overnight). CC was around .5 - probably less, but I used the smaller water sample so can't be sure, but it hardly turned pink when adding the first reagent.

Funny thing is I DID smell CC while getting my water samples this morning - I recognize the smell (as different from shock smell) from when I used to homebrew and I soaked bottles in bleach water overnight.

This morning I also noticed a yellowish haze - looked like the possible beginning of a surface algae growth - in the shallow end.

Could it be I have a SURFACE growth starting, hence no water cloudiness? Would a surface growth consume FC overnight, or not so much? I am NOT very good about brushing the pool...

-Pete
 
When I chlorinated last night the pump had already turned off - it was off this morning as well. I disperse the liquid shock as best I can by pouring it in as I walk around the pool, plus a bit more at the deep end.
Click to expand...

Please always have the pump running when adding liquid chlorine. It could damage your surface. Do you have a liner, concrete, fiberglass? Can you please add your signature so it shows up in each post.

The best thing to do right now given what you have written in your posts is to SLAM to the pool. Turn the filter on and bring up to SLAM level for a few days. Once the water is clear, then perform your overnight test. If you find that you failed the OCLT at higher levels, allow the levels to drift around the 10 mark, and then perform the test again.

- - - Updated - - -

Also, can you please post a full set of results and confirm what test kit you are using?
 
Petebacher said:
This morning I took 4 measurements. 23, 24, 29, 29 at various points around the pool. A bit more widely spaced than I would have preferred, but the average of 13 was right where it should be (13.5 would have been 0 FC loss overnight). CC was around .5 - probably less, but I used the smaller water sample so can't be sure, but it hardly turned pink when adding the first reagent.

-Pete
Click to expand...

OK, I am confused for sure... I think you have been dipping into that homebrew a little too much... :p

You say you took four measurements of 23, 24, 29, 29 and then say the average is 13???????

What test kit are you using and how could you use a smaller sample?

Thanks,

Jim R.
 
Jimrahbe said:
OK, I am confused for sure... I think you have been dipping into that homebrew a little too much... :p

You say you took four measurements of 23, 24, 29, 29 and then say the average is 13???????

What test kit are you using and how could you use a smaller sample?

Thanks,

Jim R.
Click to expand...


I'm guessing those are the number of drops to titrate to clear which divided by 2 is the FCppm using a 10ml pool water sample.
 
Clear as mud, eh? Rushing to get out of the house this morning did not help, I guess...

Test kit is a Taylor K-2006. Readings are in drops, for the smaller size water sample, so (dividing by 2) they equate to: 11.5, 12, 14.5, 14.5 PPM FC.

Catanzaro: Pool is in-ground plaster. The water is crystal clear, so not much point incorporating degree of water clarity in my SLAM assessment. Pressure on my DE filter is unchanged (unlike earlier in the season, when the water clouded and the filter pressure went up noticeably). The odd point this time and reason for the post is that my FC is dropping drastically each day.

I am starting to believe my POOL WALL AND FLOOR SURFACE ALGAE diagnosis may be correct...

I'm heading out now to measure EVERYTHING. But looks like I'll be SLAMing.

-Pete
 
Pool water clarity is a difficult observation to quantify. FC loss is due to a high bio-load or sunlight degradation. Testing FC loss overnight night vs only the day light hours will help you determine the difference. Sounds to me like you had a significant bio-load event during a low FC period and you are now supporting billions of multiplying micro-organism free loaders.
 

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AM FC reading is 1/2 point HIGHER than the PM post-SLAM start reading (taken last night after about an hour of the pump running to distribute the liquid shock). Water started at 90, and the air was quite cool last night, so there was LOTS of evaporation overnight... Pump is running 24/7.

I have not yet brushed - that will have to wait until tonight...

So to re-cap...
- Water is crystal clear and filter is rock steady w/ no pressure rise
- Pool has passed the OCLT (meh - I haven't yet brushed)
- CC gets tested tomorrow morning after I get in one brushing...
 
Seems like I am on a witch hunt. For various reasons I wasn't able to actually MAINTAIN until Tuesday. Yesterday I finally had time to brush. This morning I have zero FC loss.

Old Chlorine? (I used a different brand for the SLAM). Lower CYA than I thought? I'll investigate further today...

So to re-re-cap...
- Water has been crystal clear the entire time - filter has been rock steady w/ no pressure rise
- Pool has passed the OCLT including brushing (full brushing last night - CC has been consistently negligible since Tuesday and was negligible last night)

I expect to lose lots of FC early today as my FC is currently 21 and well over the level my CYA can protect. Let's see what happens later in the day - I'm going to try to measure several times to get a better picture of my FC loss...

-Pete
 
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