Strangely low FC consumption, and now algae

[ShinDiors]

This season we got a new solar cover, and did not swim much while spending a month internationally. After we came back and doing the routine FC check and adding LC, quite a few times the consumption is low that we did not have to add FC for a day or two (CYA 30 back then, and we maintained the FC between 4-7 just to be safe), and about a week ago while brushing the pool, we noticed patches of greenish mark on the deep end where we have a return port plus a main drain. Brushed that off and found it again last weekend, so now we are in SLAM process.

Thought it was inaccuracies from the stale R0871 reagent and bought a new set, but after doing comparison, does not seem to be the case (the old reagent might need one more drop). I did not think we let the FC drift down off the mark too much before the algae (although we did realize not having to add LC as much compared to same time last year). So my question is, what might caused this problem if my FC is kept at a proper level? I have single speed pump and had it running about 11 hours a day, used a vacuum and brush it weekly (may missed one week, I think probably right before we started to see the greenish mark). Could it because of the new cover (and extended covered time) and less swimming this season?

Did not pass OLCT last night, lost about 2ppm. Solar cover was on yesterday while trying to maintain the SLAM level (too many leaves around), but I just opened it up and will leave it open today (would be a overcast and rainy day).

 

[Newdude]

Hey Shin !!!

People always miss that the water test is a momentary snapshot of that 10ml of pool. It's never perfectly uniform across the pool, even with circulation. All pools have poor circulation areas or dead zones that could be below what you're testing. And the top inch or so takes the brunt of the immediate FC loss, which is why we go elbow deep for a sample.

If you're seeing overnight loss, some part of the pool dipped too low at some point. There's no two ways about it. The fix after a completed slam is to raise the target FC a little, though with UV demand falling off a cliff right now for us, your prior targets may now be plenty.

 

[ShinDiors]

Hey Shin !!!

People always miss that the water test is a momentary snapshot of that 10ml of pool. It's never perfectly uniform across the pool, even with circulation. All pools have poor circulation areas or dead zones that could be below what you're testing. And the top inch or so takes the brunt of the immediate FC loss, which is why we go elbow deep for a sample.

If you're seeing overnight loss, some part of the pool dipped too low at some point. There's no two ways about it. The fix after a completed slam is to raise the target FC a little, though with UV demand falling off a cliff right now for us, your prior targets may now be plenty.

We just grew a bit comfortable about the routine after three seasons, thinking that as long as the FC was tested on target, there won't be a problem. Arghh.

We did follow the instruction of water sampling at elbow deep, at least 30 mins pump running. My wife took the sample at the deeper end normally, while I was doing it at the shallow/deep line. And we have mostly tested (before adding LC) the level to not below 4 (maybe one time 3.5), and added LC according to poolmatch. Now we are in paranoid mode that wanting to add LC no matter what the test says....

 

[Newdude]

Can you further explain the 4-7 target ? Many miss that too and think a 5 is fine. It may be in the evening after the days UV loss but it's probably not enough to make it through today's loss when testing in the morning.

Now we are in paranoid mode that wanting to add LC no matter what the test says....

That's why I run hot. I'm pre-covered for whatever curveballs the universe throws at me that day from a big storm, to equipment hiccups, to an impromptu get together. And if none of that happened, maybe I was too busy today and had to skip keeping tabs on it.

On the plus side, as UV demand continues to drop with shorter days and the sun getting lower in the sky, last week's dose/schedule probably provides a little safety net this week.

 

[wireform]

There's nothing wrong with adding daily what the pool seems to be consuming. There's lots of room between target and slam level.

 

[ShinDiors]

Can you further explain the 4-7 target ? Many miss that too and think a 5 is fine. It may be in the evening after the days UV loss but it's probably not enough to make it through today's loss when testing in the morning.

That's why I run hot. I'm pre-covered for whatever curveballs the universe throws at me that day from a big storm, to equipment hiccups, to an impromptu get together. And if none of that happened, maybe I was too busy today and had to skip keeping tabs on it.

On the plus side, as UV demand continues to drop with shorter days and the sun getting lower in the sky, last week's dose/schedule probably provides a little safety net this week.

Our CYA was 30, so FC 4-6 was the range, but during our international trip, we had to put quite a few pucks in the floater, so I was trying to leave some room for CYA drifting up to 40 (FC 5-7). We do water testing at dusk, and add LC afterwards, normally targeting FC 7. Our CYA was low to start with this season, and CYA test was prone to inconsistency IMHO (for example, I sometimes could not see the spot because of the reflection of light on top of the liquid level), so I wanted to play safe even if it wasted a bit LC.

 

[ShinDiors]

Noticed that the viewing window on my Pentair MPV has visible green gunk (tried out possibly, since backwashing water would not get it off). That won't affect the pool water right? How do I get it off to clean, is it threaded on (do not see any screws around)? Thanks

 

[wireform]

Noticed that the viewing window on my Pentair MPV has visible green gunk (tried out possibly, since backwashing water would not get it off). That won't affect the pool water right? How do I get it off to clean, is it threaded on (do not see any screws around)? Thanks

The sight glass will unscrew, make sure not to lose the gasket. Finger tight is all it needs.