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Bleach Dosage


Cooper772

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Tonight I tested CYA and it is very high. I'm wanting to start using bleach to bring it down, but have questions about dosage. so with the sodium dichloro-s 56% available chlorine that I have been using, I have been doing .03oz/100gal. to raise chlorine 1ppm.(maintaining it at 3-5 ppm) So if using bleach, how much do I use to raise chlorine 1ppm? And would I be correct in needing to keep an eye on the CYA level dropping so that once it is less then 30ppm I can dose with dichloro to maintain CYA within correct range? I recently did a water change, which was the first change in a brand new tub, and I did use Sea Klear. (some real nasty green greasy stuff came out)

Thanks,

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Bleach will not bring the CYA down. Only water dilution will lower it. The CYA is high because you have been using Dichlor where for every 10 ppm Free Chlorine (FC) it also adds 9 ppm Cyanuric Acid (CYA).

You can certainly switch to bleach at this point to prevent further buildup of CYA and the CYA will probably drop slowly at around 5 ppm per month (maybe more if your CYA is high). However, when using bleach you'll want your Total Alkalinity (TA) lower at around 50 ppm and you'll want to add 50 ppm borates (usually from boric acid). As for dosing, use PoolMath to calculate dosages (unlike The Pool Calculator, it is being maintained and has been updated to include 8.25% bleach). You'll need to use a larger volume to see dosages -- so 10,000 gallons would tell you 100 times the amount needed per 100 gallons so for 1 ppm FC that is 0.024 ounces weight (around 0.023 fluid ounces volume) of Dichlor or 0.15 fluid ounces of 8.25% bleach. For a 350 gallon spa, this translates into roughly 1/2 teaspoon of Dichlor or 1 tablespoon of 8.25% bleach.

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  • 3 weeks later...

So I think I'm going to do a water change soon to try to get CYA in check and start using bleach once CYA gets built up. Should I just use borax that you can get from walmart our something different, I have found online hexaborate should I use that. Also using pool math with spa size being 400 gal it says to use 15 oz by weight or 16 by volume boric acid to get 50 ppm. Is that calculation correct? I'm using the calculator on a ipad so just want to make sure it works. As always thanks for the help!!!

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It's easiest to add boric acid directly since it doesn't require acid and doesn't change the pH very much. You can get it at DudaDiesel, The Chemistry Store or AAA Chemicals (large size only, so really only for pools).

You can get 20 Mule Team Borax from the grocery store (or Walmart), but you would then also need to add acid and should split the dosage alternating 1/3rd or 1/4th doses back and forth between borax and acid. Borax raises the pH significantly by itself.

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Chem geek, thank you for all your help. I have ordered boric acid, and now Im looking for a testing method. Reading some reviews on test strips, Im finding that many say its somewhat of an issue comparing colors on the strips. I have seen discussion on a couple different forums about the drop test sold by a company in Canada, but following the link does not take me to the actual test. I think the most recent discussion I have found was in 2012. Is this test something that is still available? Between the two test kits I have already for testing my water I basically have the K-2006 test kit (K-1005 i-care, and K-1515-c FAS-DPD CHLORIEN TEST) so Im only missing S-0009 and S-0010 If I can't get the borate drop kit is there a way to get the needed reagents to perform the test?

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The Canada company doesn't sell that test kit anymore. I have it and it is nice, but the test strips are OK to use and yes they can be a bit hard to read. Fortunately, accuracy for borates isn't critical and most importantly if you dose properly then you know the level. So for a spa having a borate test isn't that important. There are no borates in the fill water so you just dose properly and you can be assured you have what you want.

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Hot tub is currently warming up from a fresh refill. I have started testing the water and come up with a couple questions. water temp at time of test was 68, TA=60ppm, is that acceptable for using the dichlor then bleach method or should I for sure lower it to 50? pH=8.6 will lowering the pH using Sodium Bisulfate also lower the TA closer to 50ppm? Second question is CH is 70ppm, and I do not have any Calcium Chloride on hand, small town I live has no pool supply shops, but tomorrow afternoon I will have a chance to buy some. My question is if I go ahead and adjust everything, TA,pH,add Boric Acid, shock to 10ppm, then raise the CH tomorrow afternoon, will I be ok, or do I need to wait until I can raise it before I go any further? As always thanks in advance for the help!!

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You can certainly see how 60 ppm goes and Dichlor will lower the TA anyway. It's only when you switch to bleach that the TA shouldn't change much at all. And yes, adding acid will also lower the TA along with the pH.

As for CH, you only need to increase that if you have a problem with foaming. The purpose of 120-150 ppm CH is to reduce foaming. You don't need to wait for the CH before using the spa.

If this is a new spa or if the chlorine was zero for too long then you might consider using Ahh-Some® to remove biofilms, though you could just see how things go and do this before you dump the water at the end of this water change cycle. Use of this product requires dumping the water after its use (when using it at high doses to remove existing biofilms).

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