FC loss versus CYA level

[mas985]

Then the theory is incomplete. As was speculated in that post, there is clearly something else going on.

As for the dispersing, the dye test is difficult to quantify concentration. You know the dye gets everywhere fairly quickly but the concentration is not known all that well. If you are interested in determining the actual concentration of FC, why not measure it directly. Add enough chlorine to double the FC in the pool, then at constant intervals, measure the FC at multiple locations around the pool and find out how long it takes until you cannot measure a difference.

 

[davethomaspilot]

So, at JoyFulNoise's suggestion, this morning I tested for CC in addition to FC. I quit doing that since it seemed always to be zero.

This morning, FC is 1.6 pmm and CC is .2 ppm.

Now that CC is non-zero, I'll go back and read some more posts to figure out what that means.

 

[davethomaspilot]

It's not that easy to quickly measure FC in multiple locations. Walking around the pool to get the samples would stir things up, I think.

Use of the dye first might give me a clue on where to find the biggest differences. Then maybe try measuring FC dispersion to the worst case spots.

- - - Updated - - -

CC = .2 might mean dead frogs in the skimmers.

Four this morning. Not uncommon lately here in North Carolina.

 

[JoyfulNoise]

Dave,

Higher levels of chlorine will also increase the chances of you detecting CCs because the oxidation rate increases. One thing you could do is a bucket test - get a 5 gal bucket and put 4 gallons of pool water into it. 1/4 teaspoon of of 8.25% Clorox bleach should raise the FC level to 10ppm (that would be shock level for a pool with zero CYA). You could then test for CCs right away and see how high they go.

As for water sampling, make a draw tube out of 3/4" PVC pipe, like this -

The tube lets me sample water from 4ft below the surface so I know I'm always testing bulk pool water.

 

[mas985]

It's not that easy to quickly measure FC in multiple locations. Walking around the pool to get the samples would stir things up, I think.

I meant just around the edge of the pool. I think that's where most dead spots would occur anyway.

 

[JVTrain]

Dave,

Higher levels of chlorine will also increase the chances of you detecting CCs because the oxidation rate increases. One thing you could do is a bucket test - get a 5 gal bucket and put 4 gallons of pool water into it. 1/4 teaspoon of of 8.25% Clorox bleach should raise the FC level to 10ppm (that would be shock level for a pool with zero CYA). You could then test for CCs right away and see how high they go.

As for water sampling, make a draw tube out of 3/4" PVC pipe, like this -

The tube lets me sample water from 4ft below the surface so I know I'm always testing bulk pool water.

I'll get mine made that way one of these days. Still using the thumb method.

 

[JoyfulNoise]

I'll get mine made that way one of these days. Still using the thumb method.

Yeah, it's like $6 worth of PVC parts from Ace Hardware. I think the most expensive piece was the grey CPVC sch80 hose barb fitting on the end. I only added that because it makes it easier to drain the water into a Leslie's water sample bottle and they did not have any in regular PVC.

 

[BuckeyeChris]

I did read that. That's the opposite of what theory would predict. The higher the CYA, the MORE chlorine should be used (in absolute terms).

The running theory is that, on top of the chemical protection that the CYA provides the chlorine, the CYA actually provides a direct deflection or absorbtion of the UV, preventing it from penetrating the pool as deeply as it would in a lower concentration.

 

[davethomaspilot]

Hey, never saw the draw tube before.

Probably "non-newbies" new about how to do that, but I didn't. I have plenty of pvc and ball valves laying around to make one with.

Thanks!

 

[JoyfulNoise]

Hey, never saw the draw tube before.

Probably "non-newbies" new about how to do that, but I didn't. I have plenty of pvc and ball valves laying around to make one with.

Thanks!

You're welcome.

Plenty of great ideas on this forum. Try searching for "DIY Pool Cooler" in the search bar and see all the ingenious water fountains and showers people have come up with for plugging into return lines.