Hi

Newbie here Many thanks for this great forum to help me.

I was about to shock my Salt Water Pool so thought the best place to read up on it was here but now I am more confused than ever

My CYA is about 70-80
My FC based on the recommendations here is being kept around 5-6FC
My CC is about .2
BUT My overnight FC drop is about 1.5 -2.0FC

My pool is clear but get a lot of dead algea dust on the bottom it has also been super hot here recently

If I use the table here on shock level based on my CYA level i would have to raise the FC to about 30FC however not one product recommends this. I even caontacted HTH and they could not understand this. According to them I should be only shocking to a level of 5FC which I already am at I was told I run the risk of damaging equipment at this level.

I have just exhausted Google trying to get an answer

Is this reading of 30 meant for NON salt water pools?

The majority of the pool industry is in denial about what CYA does. When CYA is around 70 to 80 you need to use much higher FC levels than you would need to use when CYA is lower. However much of the pool industry simply takes the numbers that would work if CYA was zero, and repeats them regardless of the CYA level. Obviously shocking to 5 will not work. If it would work it would have already worked for you.

There is no risk what so ever to the equipment of having FC around 30 when CYA is 70 or 80. There would be a risk if CYA was actually zero.

Welcome to the forum. +1

Unless you bring your FC up to that 30ppm value (and HOLD IT there until you pass the OCLT), you will simply continue to stay stuck using additional chlorine to fight the algae (and subsequent "dust") you are seeing.

Yeah, that. Unless you want to drain your pool to get your CYA back to zero, which is NOT recommended

Welcome to the forum Michaelandliz

Trust what you are reading here in pool school. look what you are going through right now and then read some of the threads here. If you want a clean and trouble free pool follow the advice, it's free and it works.

Did I mention read POOL SCHOOL?

wow -ok thanks for the help, thats a heck of a lot of chlorine I need to add to 17,000gals

My other concern is I have a 3 year old daughter that swims daily, when I have shocked before to about 12FC following the companies guidelines it takes about 3 days for the FC to drop back to about 5. I could never let our Daughter swim in 30FC and I fear the pool would be closed for weeks while i wait for it to drop back down.

Sorry if these sounds like amateur concerns to the professionals but i am thinking of living with a bit of dust rather than filling the pool with so much chlorine. The pool is crystal clear and the CC was 0 this morning although I lost about 1.5FC overnight which of course tells me there is a bio load.

The SWG is set to 50% and the pool pump is on for 11 hours a day. we have had scorching weather here the past 3 weeks and the pool is in constant full sun, the pool temp is averaging 86F daily.

In a complete conundrum what is best.

That's a pretty big drop overnight.

It's safe to swim up to shock levels. And if you shut off the SWG FC should come down really fast anyway.

You're walking a tightrope. At least crank up the SWG or dump in some bleach to get FC to 9 or 10, same level as a non-SWG pool should have.

I will likely follow the advise then and put in the bleach I have found the pool calculator to work out how much.

My other concern is bleaching my lovely deep blue liner.

How are you testing to have determined what your overnight loss is? It does sound like you need to follow the shock process per instructions on this site (because you mention seeing algae), but I am curious how you are testing.

I am using the taylor test kit and testing using the 25ml more accurate .2 drip rate.

wow ok so according to the chart i need 7 gallons of bleach at 6% strength.

Sounds ok. If you buy 12%, you could use half as much.

Don't forget...when the FC drops below the shock value for YOUR CYA, it's safe for DD to swim.

Welcome to tfp, Michaelandliz

I would switch to the 10 ml sample and save your reagents. Each drop will then be 0.5 ppm, which is more than enough accuracy for proper chlorine maintenance. See: http://www.troublefreepool.com/extended-test-kit-directions-t25081.html#p206393

Since we do not know the volume of your pool, we can only guess. If your pool is 20000 gallons, then to get 21 ppm (FC shock level for 80 ppm per poolcalculator.com), you would add 871 ounces (about 6.75 gallons) of 6% Bleach. Is your pool 20000 gallons?

Please put your pool and equipment details in your signature. It help us help you.

Hiya

thanks for your help

my pool is approx 17,000 gallons its kidney shaped with a hump (no I dont mean its upset with me )and 36x16 and about 8' deep end and 3' shallow

equipment
Pool liner
mainly haywood
gas heater
5 x Heliocol solar panels
1hp super pump (to be replaced soon with something quiet!)
sand filter
SWG
Pro logic controller

Looks to me like you need 600 oz (just under 5 gal) of 6% bleach to get to your shock target of 21. You will need some extra on hand to keep it there, which you need to do until your pass OCLT, Water is clear and CC .5 or less.

This is one of those cases where I would just get 12.5% Liquid Chlorine from a high volume source, as it will be a lot less to transport. I would get 4 gallons, as you have an SWG, and hope not to shock again anytime soon. 12.5% not not have as good a shelf life as 6% Bleach.

Hi

thanks for your help.

I read the CYA/FC chart and it said 30 for SWG pools, whats the reason for 21? of course I prefer this lower number

My pool is crystal clear and my CC was 0 as of this morning even on the 25ml more sensitive test, I just get FC loss overnight on several tests. I also get the brown dust, but after vacuming twice with a electical robot vac with hyper filtration that seems to have deminished by 75%. So the main issue is FC loss.

I used your 17,000 Gallons, and a CYA of 80, in the Pool Calculator.

I got the 30Fc from the pool school table
pool-school/chlorine_cya_chart_shock

So which is right?

sorry to be a pain.

They are both right. In any normal situation either number will work, though the Pool School numbers will work more quickly. The chart in Pool School is a little more conservative, i.e. reduces the odds of there being a problem.

Ok that makes sense to confused old me now, ok will go by 21 (yeah less chlorine to add )

I will do another FC test overnight just to be quadruple sure I actually need to do this as my CC is 0 and do have a crystal pool, I will also not vac the pool and see what shows up.

Now you know why I have done everything possible to make sure I never have to shock again. Imagine how much it took me to shock my pool for two weeks!