Filtration's effect on chlorine demand?

[sbcpool]

I installed a new Intelliflo a couple of weeks ago. Coming from a single-speed power hog it's been relatively nice so far. I am taking advantage of the increased efficiency by doing low flow for long periods.

The other day I noticed a change in my pool - I caught a whiff of chlorine while walking by. I got out the test kit and my FC was 10.4!!! Still within SLAM levels, but WAY higher than normal. I haven't changed chlorine brands or dosing. My only theory is that the increased filtration from longer pump run times has dramatically decreased chlorine demand. I am now only losing about 10% per day where I was losing 30 - 33% per day with CYA ~60.

Is my hypothesis plausible, or could it be something else?

 

[JoyfulNoise]

Hmmmmm....wouldn’t have expected that.

Is the SWG gone?

Have you seen any return of mustard algae?

 

[sbcpool]

SWG is gone for about 3 weeks now. Even at FC 10 I still see the very slightest, barely detectable yellow on the shaded walls after a couple of weeks. You can't see it when it's on the wall, but when I brush I can see a very faint (barely perceptible) yellow cloud rise in the wake of the brush.

 

[mknauss]

Is it smoky in your area? That really impacts UV on your pool water surface.

 

[sbcpool]

Is it smoky in your area? That really impacts UV on your pool water surface.

Very. Even though the air temp has been in the mid 90's my pool dropped from 84 to 72 degrees in a week.

 

[mknauss]

That's it. We had a few days of heavy smoke before the last cold front and our pool water temp dropped like that. I put the cover on.

 

[sbcpool]

My UV sensor registers a UV index of 2 - 3 for the last week as opposed to 4 - 5 the week before. Makes sense. I never thought of correlating my UV sensor data with FC degradation.

 

[sbcpool]

If I average the 5-minute UV index for all hours that sunlight is on the pool it seems that my pool sees about 1% FC loss for each unit of UV index/hour. In other words, if a day sees 30 UV index hours my pool loses about 30% FC. If it's 10 my pool loses about 10% FC.

 

[Oly]

Yes I too have seen a fall off of FC usage per day due to reduced solar radiation from smoke. Pool temps also falling.