I believe you wrote that your CYA was in the 40-60 ppm range so your current 20 ppm FC is in the ballpark of regular shock level. You can let it drop to around half this amount, so 10 ppm FC, and close the pool if the water is cold, preferably 50ºF or lower. If the water temp is higher, then it's unlikely for the chlorine to last very long. Also, the rate of cover degradation is not just based on the FC/CYA level, but also on temperature. It is true that the cover will degrade more quickly at a higher FC level compared to the 1-2 ppm FC you were told to use, but there's no way your chlorine will last through the winter so you are much more likely to open with algae or a bacterial conversion of CYA possibly into ammonia.
I suggest you follow this post for closing so let your chlorine level drop to around 10 ppm FC, add Polyquat 60, and do this when the water temp is cold. Then if you find that your chlorine level lasts through to spring opening when you open the pool before the water warms up, you can try the following season just using chlorine and not needing the Polyquat (up to you).
Thanks, I'll go with your (Buckman Labs) suggestion above.
I just don't want to wait much longer since the water is too cold to swim.
Guys who closed my pool used something called AquaZone. I don't know the FC level I had at the time of closing, maybe around 3-5, but I still had some when I opened pool in May and water was crystal clear. The AquaZone box contains Winterizing Powder (not sure what's in it) and Liquid Winterizer (alkyl dimethul benzyl ammonium chloride). Any comments on AquaZone product?
The Winterizing Powder was probably non-chlorine shock (MPS) while the Liquid Winterizer is a linear quat algaecide. Linear quat algaecides can foam and they break down faster from chlorine which is why we recommend Polyquat instead. The water must have been very cold (40ºF or so) to have the FC last that long. If the water were 50ºF you might lose 35% of the FC per month.
Leslie's Algae Control is 60% Polyquat. See this link for instructions on closing the pool using chlorine and Polyquat algaecide. The maximum dose for Polyquat 60 is 16 ounces per 10,000 gallons (that's a little more than the 1 quart per 25,000 gallons on your label). So follow the Buckman Labs instructions and use the maximum dose allowed.
My pump started acting up, so I decided not to wait much longer and closed. I shocked about 10 days ago.
It's been in 60s lately and I wasn't loosing much chlorine. I may have added about 5 96oz 6% in 10 days or so to keep it above 5. (my CYA is around 50, maybe 40)
I had 5 ppm on Wednesday, then didn't add any more chlorine because I didn't run the pump as much. I had about 4.5 Friday when I added about 40 oz of PolyQuat 60 and ran the pump. Closed and covered on Saturday with water temp around 65. I lowered the water about 12" (below returns) and then added about 8" (2-3" below skimmer)
Results from Sunday with TF100. I think some agents are from last year.
FC 1.0 (about the same with taylor purchased this year)
CC <= 1 (same as it always been)
I'm not sure how many gallons the 8" of water is, but from 4.5 to 1 ppm? Did I manage to get algae as I was closing? If so, could it come from the vac line which I didn't use at all or from the cover which I washed both sides in May? Could it come from 1 dead mouse I found in the pool on Saturday?
I can add some chlorine and mix it by blowing the main drain if that's what I should do. I can also add more PolyQuat if that's preferred.
Just not sure how long I should be blowing main drain for to get it mixed well.
Blowing main drain seems to be pretty easy to do - just hook up compressor to the pump's drain and open the valve. If blowing the main drain is good enough to dilute chlorine, why not keep the level at 2ppm and then just add chlorine when needed?
Or I can just leave it as is and see what happens. I have 2qt of algaecide left to combat algae in May
P.S. Is PolyQuat 60 an alternative to Chlorine for closing? What's the benefit of using PolyQuat instead of Chlroine and vise versa? Cost vise, the 40oz of PolyQuat ended up costing me about $16-17 with tax
Chlorine slowly oxidizes Polyquat, but generally Polyquat lasts longer than chlorine especially in sunlight. The main advantage of using Polyquat on closing is that in a pool exposed to any sunlight, the Polyquat will last, especially if the water is cold, so will help to prevent algae growth even if the chlorine level gets to 0. If you cover a pool and close it when cold, then chlorine can last a long time.
You can raise the FC again if you like, but if the pool is exposed to sunlight then it's going to drop again.
It's not exposed to sunlight. I have solid cover. But it looks like PolyQuat brings the chlorine level down, right?
So is it worth adding chlorine while the pool is covered? If so, what should I be bringing it up to and when, assuming I have 40oz of polyquat in it(maybe a bit less due to partial drain and refill of about 8") 1ppm of chlorine and water temperature today is around 65? It'd really take me 5 min to do it, plus whatever time I'd need to dilute it
According to Buckman Labs who make Polyquat, the higher levels of chlorine with higher levels of Polyquat have the Polyquat get broken up into smaller pieces, but they are still effective (eventually they break down further but that is much slower) so having chlorine with Polyquat still works. It's also possible that you had something else in your pool consuming chlorine -- not the Polyquat.
As for adding chlorine when the pool is covered, the main issue is that of circulation. If you had circulation, then adding chlorine is no problem, but without circulation it would be too strong in one area and not strong enough everywhere else. I wasn't clear if you are winterizing your pool lowering the water level, blowing out and sealing the lines, and turning off the pump or if you do not get hard freezes and were just reducing pump runtime. If the latter, you could certainly add chlorine over the winter. That's what I do and I lose only around 1ºF every 2 weeks when the water gets to 50ºF or so.
The lines are blown out and plugged, except the main drain of course, which was blown and (hopefully) air tight (jandy valve). I can't run the pump, but I can blow out main drain again and that should move water around a bit. That's what I was asking - is it worth doing it, assuming I have 40oz of polyquat in it and 1ppm of chlorine with water temp 65. I have 2 main drains on the bottom of the pool but when I blow them out with 5-20psi (through the pump's drain), the air is coming out from closer one only and it's not like tsunami I'd get with mighty vac or cyclone blower (plus the blowers reach 2nd drain), but the water is still moving a bit. I don't know if I should try higher psi, but I heard people do it even at over 100 and never had issues.