Re: Unexplained FC Consumption (updated title)
I am a bit confused now
I do think it was you that posted a bit of borates actually cause algae...is this true and where did you find that ? Was it in the 26 page thread, that I have actually read a while ago but of course forgot most of the details.
Chemgeek's post #198 in that thread indicates that low borates, below 30ppm, can be food for algae, somewhat like phosphates. But is irrelevant in a properly chlorinated pool. So they do not directly result in algae growth. At and above around 30ppm, they begin to yield algistatic properties.
He doesn't say that it creates a Cl load, or reduces cya, which is what's going on.
What sort of cover do you have? IIRC it's just a solar cover, is it completely opaque? If it isn't, then your pool is getting UV, this is eating the your FC during the day, consuming Cl from the Stenner.
30ppm cya is QUITE LOW, with water temps hitting 90deg.
This would explain your high daytime loss, and low nighttime loss. Raise your cya, and logic dictates, assuming there are no other issues at hand, as yet to be discovered, that the problem should then go away.
I would ask why you are running such a low cya in the 1st place? Ie. What is your reasoning for this?
The more sun, heat, and hotter the water temps, the more cya you need, to a point. I'd say you need to be shooting for a cya level of 50ppm, adjusting your Stenner accordingly to maintain FC levels decently above minimum.
It seems to me, being incredibly analytical myself, that this problem has become too complicated, and is really just something as basic as too low a cya for this years weather. Many people on TFP, myself included, are experiencing higher than usual FC loss this summer, over prior summers that is. So this would not be out of line.
EDIT: As for the stuff on the bottom of the pool, I get that too, it's fine fine dirt that blows into the pool, and falls out of solution, precipitating to the pool floor before the filter can catch it all. I was able to determine this by actually getting in the pool, very slowly, and analyzing it on the floor of the pool. Different dirt has different properties, but this fine dirt where I live actually behaves in an interlocking fashion like sand in that it seems to "cling" to the pool floor like it's somehow sticky. In fact, it likely is just very very fine sand.
If I disturb it with the motion of the brush, it disappears into solution. Even my rover can't get it all, as it has no brushes and the substance is otherwise too sticky for it all to release when the suction of the robot slowly passes over it.
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