Either will work, but the FC levels from that page are more "conservative" than the pool calculator. Those levels are from this page which is ChemGeek's expanded CYA/Chlorine chart.

The levels in the chlorine chart are higher than pool calculator's, by a small amount at low levels (up to 40ppm CYA), a wider range at mid range levels, and then they are actually lower than the pool calculator at very high CYA levels.

They both work, and the general rule of thumb around here is that either is fine but if the lower values from the pool calculator aren't working, try the higher levels from the chart. I wish I had a better explanation of it all, sorry. It's a little confusing to me, still. However I have been assured that both sources are valid. I choose to stick with pool calculator for simplicity sake.

I would do the 20ppm personally. Maybe find a happy medium and shoot for 24ppm?

ok I started running the filter and shocked the hot tub alone for now, tomorrow i might join the two but wanted to at least clean some of it off first. Its hard to figure out how much shock u need when u dont have any way to measure I decided to go with 24 shock for 1000 gallon spa, showed 1.4oz and 1.8oz for the two so for my chemical I went with 1.6oz but really i estimated a bit not having a measuring a cup. Tomorrow I might just shock the whole pool to make it easier. I turned the swg off to 0%.

Ok I shocked last night to I guess somewhere around 24, just checked FC and it is back to 17 after 34 drops around 10AM this morning, I shocked again. I did not bother checking before sun gets up as I figured I cant fix the problem in one night. The water in tub and basket now looks crystal clear. Do you guys think I should run one more day before combining with pool shocking or do it now before FC in pool drops too low?
Also when I get done should I backwash the filter?

Not likely, plus you're still losing chlorine rather fast. Not done yet.



I would do it all now. No sense wasting the chlorine.



Yes. You might want to do it now even. Check the pressure. When it rises above your threshold, it's time to backwash.

Just checked the FC and it reads 23, I assume it might have lost some but very little as I shocked to about 24 this morning. Do you guys think I should sock again at all, since pool calculator states to shock to 20 anyhow? or just read tomorrow AM before sun and if it is still 23 or 22 then it means I'm in the clear? I forgot my filter turns off at 3 so untill 7:30 it was running on spa pump only :/
frog when u say backwash now, do you mean backwash again when its all done or just once now? my pressure has not reached max since i backwasher a month or two ago and i am not sure if my gauge is working properly at all anyhow. Is there any other way to tell if pressure has built up? i did backwash during the season since I had to shock once as my CYA was low and FC was 0 and then once again for some other reason.

Apparently the gauges go bad frequently, but replacing it is a cheap way to prevent damage and to find out if it actually is bad.

I haven't used a sand filter personally yet (although I do own one, next season) but I'm fairly certain most people backwash them frequently, even once a week. But most certainly more frequent while shocking. The algae dies, leaves the white/grey carcasses and that has to be filtered out. People speak of backwashing the filter a few times a day while shocking. It can't hurt, so why not? The fact that the pressure never rises even while shocking is suspicious of a faulty gauge and I'd change that too.

As far as the pool, it sounds like it's not losing chlorine very fast. I'd do as you suggested. Check tonight after dark and run the OCLT on both the pool and the spa. Do separate tests for each but run everything together at shock level (20ppm). I think 20ppm is plenty high for your pool, you aren't dealing with a swamp and the amount of water that had algae is small. Mix that all up together for one night and see what happens. I think you may be able to enjoy this little baby shock and be done tomorrow morning. If you're worried or don't pass any one of the 3 criteria, go another day.

Ok so I am done with shocking and just backwashed the filter, I thought after backwashing you need to run the filter for 24 hours, at least that's what I thought I read in the past...... but now i can not find this information anywhere..... is it true or can I turn my filter off after a couple hours? Thanks for all the help guys by the way, and frog thangs for convincing me to get the test kit

After a backwash you can immediately go back to your normal run schedule.

Thanks Bama ! I am glad you say that because since I did not get a reply last night I shut off the filter around midnight it came back on 7am according to schedule. Can you recommend how often I should turn on the spa blower during the season to avoid the same problem next season ? We really do not use the hot tub at all, although next season that might change, so I need to periodically manually turn it on to circulate the water, unfortunately that motor is not on a timer.
On another hand I bought the antifreeze yesterday for the closing and on package it states its good for all pipes except acetate or something like that...... now I think I have regular PVC piping but never heard of acetate, do you guys have any idea what those are? I do not want to accidentally cause any problems in case I do have them.

I'd run it at least an hour or two every day. I'd consider adding a timer for it so you don't have to try and remember to turn it on and off each day.

o man that would be a pain, it would also mean turning the pump on each evening when i get home, unless I just run the blower for an hour to circulate the water from pool...... my equipment is behind my back yard, have to get through 2 gates its not something that I would be looking forward to. I might install the timer as you suggest or probably do it weekends only untill I do so..... I was kinda hoping once in a while would be ur answer