Chlorine

What is floc, clarifier, stabilizer, cyanuric acid,
algaecide, brightener, dichlor, sodium hypo,
sodium bisulfate, ....??
momoffour
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My Pool: 24 ft. round above ground with vinyl liner, 2hp sand filter
Location: Haslet Texas

Chlorine

Postby momoffour » Mon 22 Jun, 2009 11:55

I added one bag of HTH 49% available chlorine to my pool Sunday morning at 10:00. It raised the FC and TC to 5. By Monday morning (this morning) at 11:00 the FC and TC were at .5 or less. I am using a DPD test but I test every day and try to stay on top of the chlorine.

My numbers are
TA 100
Ph 7.6
CYA 40 (although the pool place says it is 60)

I was wondering if it is normal to have to add chlorine every day. It seems to burn up very fast but the pool is in full sun and above ground. I never have a problem with my FC and TC matching when I test it or when I take a sample to the pool store and they use the DPD-FAS test. It is much easier to manage the chlorine when I have the trichlor tabs in the floater in the pool but I took it out because I didn't want the CYA to be too high.

What do you suggest? I think I might try to find cal-hypo tabs or some other tabs without the CYA (lithium). It may be cheaper and easier in the long run because of the slow release. At least I could maintain 1-2 ppm chlorine and not have to add as much powder to assure I don't let my FC bottom out and maintain my 3-5 ppm. I REALLY don't want to have to fight algae.

Thanks!!!


chem geek
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Location: San Rafael, California

Chlorine

Postby chem geek » Mon 22 Jun, 2009 13:51

You are describing the primary dilemma in chlorine choices. The Trichlor tabs/pucks are convenient because they are slow-dissolving, usually lasting around 5 days (though with enough tabs and a low setting one can get to a week or more). Unfortunately, Trichlor also increases the CYA level over time unless there is significant water dilution. So to prevent algae growth, an algaecide or phosphate remover is usually required, at extra cost and even then one can eventually run into problems if there is very little dilution. It's certainly an option -- what is important is that you understand the consequences of each approach.

Usually, even in direct full sun all day, the chlorine loss isn't more than around 50% of the FC level if the CYA is at least in the 30-50 ppm range. Some people keep their CYA in the 70-80 ppm range similar to saltwater chlorine generator (SWG) pools and only have a 15%-25% loss in FC per day. However, you have to be very diligent at keeping the FC up in such a situation. If you had a pool cover, you could probably only have to add chlorine twice a week instead of every day or two.

With your specific situation, it sounds to me as if you are still fighting algae even if it isn't visible. You can see if this is true by doing an overnight chlorine test. Add chlorine after the sun goes down, run the pump for an hour, and measure the FC level at a couple of places in the pool. Then, before the sun hits the pool (significantly) in the morning, measure the FC again. If the drop is > 1 ppm FC, then you are fighting algae or otherwise oxidizing some organics in your pool and need to shock with a higher chlorine level.

You really need to get your own good test kit, either the Taylor K-2006 you can get at a good online price here or the TF100 from tftestkits.net here with the latter kit having 36% more volume of reagents so is less expensive per test.

Read the Pool School to learn about the proper FC level to maintain for the CYA level. Also, you can use 50 ppm Borates in the pool as insurance against runaway algae growth as it is a mild algaecide and a one-time application (except for makeup for dilution). Unlike a copper-based algaecide, it won't stain and unlike a PolyQuat 60 algaecide, it won't require weekly addition and unlike a phosphate remover, it won't require removal of precipitated material.

Richard
momoffour
Pool Newbie
Pool Newbie
Posts: 3
Joined: Wed 03 Jun, 2009 22:21
My Pool: 24 ft. round above ground with vinyl liner, 2hp sand filter
Location: Haslet Texas

Chlorine

Postby momoffour » Mon 22 Jun, 2009 19:00

That is what I thought but it is wierd because the water is crystal clear. I tested the theory by adding 2 1 ib. bags 49% available chlorine and 1 1 lb. bag 70% available chlorine at 12:00 noon and when I tested at 5:00 p.m. I got 2 ppm FC and it looked like 2 ppm TC. I shocked at 10-12 ppm by my calculations and should not have a FC level that low. Should I continue to shock until the chlorine holds? I have been adding an algaeguard after I shock.

Thanks so much!!!!

Heather
chem geek
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Location: San Rafael, California

Chlorine

Postby chem geek » Mon 22 Jun, 2009 21:22

If the algaeguard is something like PolyQuat 60, then it will use up chlorine, especially at shock levels. You shouldn't need to use it if you maintain a proper chlorine level. If the product you are using is HTH Algae Guard, then this is a linear quat (Alkyl dimethyl benzyl ammonium chloride or ADBAC) and it too will slowly break down with chlorine so at shock levels the chlorine may get used up more quickly with this algaecide in the water. Nevertheless, the kind of rapid drop you are seeing seems too high unless you are overdosing with algaecide. Note that this algaecide tends to foam (PolyQuat does not, but is more expensive).

Again, an overnight chlorine drop test using an accurate FAS-DPD chlorine test kit will tell you if its sunlight or something in your water consuming chlorine.

Keep in mind that the Cal-Hypo will be increasing your Calcium Hardness (CH). It might be low if you have a vinyl pool and your fill water is low in CH. The following are chemical facts for different sources of chlorine:

For every 10 ppm Free Chlorine (FC) added by Trichlor, it also increases Cyanuric Acid (CYA) by 6 ppm.
For every 10 ppm FC added by Dichlor, it also increases CYA by 9 ppm.
For every 10 ppm FC added by Cal-Hypo, it also increases Calcium Hardness (CH) by 7 ppm.

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