How high to SLAM?

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RJPassan

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Sep 19, 2014
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Bethlehem, PA
Greetings!

Rick here. I'm new to the site but have been taking care of our pool for 19 years. We have a 23,500 gallon plaster pool in Bethlehem, PA. Hayward 1.5 HP single stage pump, Hayward DE Filter, Polaris Pool Cleaner. My wife pretty much did the chemical thing until about 4 years ago (I just did the heavy stuff). I then took over the whole deal and got water tested at Leslie's and an independent store. Sometimes went to 3 stores, got 3 different results and wondered which (if any) was correct. Willow Park Pools has a computer test program ... WaterLink DataMate 10, but it seems inaccurate as well.

We are looking to replaster (or Diamond Brite) so I thought I'd test myself and save the above hassle. I bought a TF-100 Kit and have been using it for a few days. We've put the replaster off until next year, but I am getting ready to close and have some questions. I see the advice to wait until water is below 60 degrees, and open before it gets above 60 degrees ... and it certainly makes sense. We normally close later September and open later May (8 months closed!) ... water temp above 60 in both instances ... "knock on wood" we've never had any algae problems ... water always clear... so far anyway:) We've always used the 3" Trichlor pucks which I've stopped doing per this site. Started using 8% bleach now.

We normally shock before closing (Dichlor Shock) and add polyquat algaecide. With my high CYA, I want to know how high to shock and how low to let it drop before closing?
My numbers per the TF-100:
ph 7.6
Free Chlorine 8 (per this site I've started adjusting it up to around 10)
Combined Chlorine 0.5
Hardness 350
Alkalinity 100
CYA 100

My water is very clear ... no problems we can see ... we get lots of sun daily. Per the CYA/Chlorine chart on this site, free chlorine should be 7 min, 12 target, and 39 shock. I realize that 39 is too high to boost it, so I wonder how high to raise it before closing? I calculated the boost that the shock we usually used (dichlor) raised the free chlorine, and I figure it gave a boost of around 8.

Also, how low to let it drop before closing ... realizing high chlorine is hard on the pool cover and can render algaecide ineffective?

Thanks much for all of the info on this site, and for any help with the above.
Regards, Rick
 
Welcome to TFP Rick !
You can reach your shock level of 39 with bleach or liquid chlorine 10%-12.5%. Pool Math will tell you how much to add. It's going to take some but you can get it there. That's the problem with high CYA levels. Takes a lot of bleach to reach shock level as your seeing. Next year your going to get your CYA level down to 40-50.
No reason to let it drift down to close. Your CYA acts as a buffer for the chlorine. It takes the harshness out of it. You can swim in FC levels up to shock level for your CYA level, so your cover will be fine.
The algicide is optional. I don't use it and open to clear water with measurable FC. I take mine right to shock level and forget about it.
Looks like you have done some homework reading on the site and have an understanding of what pucks do to your water chemistry. Congrats on that. Stick with our methods and having the best test kit you can get will lead you to a Trouble Free Pool ! ?
 
One minor problem is that you're reporting a CYA of 100. That's the upper limit of the turbidity test. Your water could be quite a bit higher (150ppm or 200ppm) and the test would still say 100ppm. You need to do a dilution test to see how bad your CYA really is considering your past use of stabilized solid chlorine products. If you are well above 100ppm, then 38ppm FC may not cut it.
 
Yup, as has been pointed out 100 is the limit of the CYA test, so you have to do a diluted test. While the full instructions are in the Pool School, here is the short version. Mix 50% pool water with 50% tap water. Use this mixed sample as your test water. If still at a 100 you will need to dilute more. Here is a great chart by JamesW to explain dilution rates and what you multiply the results by to get an approximation of your CYA level.

Pool water......Tap or distilled water.........Multiply result by

....1...................1................................2
....1...................2................................3
....1...................4................................5
 
Thanks for all of the great info everyone! I did the "dilution" CYA test and I'm indeed about 100 CYA. I also did an OCLT last nite and there does not appear to be anything growing in my pool (level stayed the same). My wife agrees that this is the clearest water we've ever had in the pool (19 years). That's good and bad ... good with crystal clear water ... bad as our 19 year old plaster looks worse than ever:cool:

With no algae growing, I'd still like to SLAM b4 closing. Think I should go to 39FC or perhaps 25FC (with no algae)? I also want to add Polyquat for insurance. Should I close at SLAM level, or let it drift down to preserve Polyquat?

Thanks much for the help and info!
Regards, Rick
 
Close at shock level ! Use 39-40 for you shock level since your CYA level is close to 100. You could go without the polyquat. It's your call.The water temp is key! Below 60 to close and open. ?
 
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