Normal range of hypochlorite use??

[ErniesPool]

I have a 25,000 gal in ground plaster pool, CYA = 45-50, CA = 270. Totl AL = 70 pH = 7.5. I went through a shock and it finally stabilized at 22.5 ppm overnight. Then, the next day the FC plummeted to 12 during the day. Today it fell to 3 even after adding 2 quarts of bleach (8.25%).

This seems to be a large amount of chlorine usage. What is the normal chlorine usage for a pool this size in the summer????

 

[jblizzle]

Well, we usually say 2-3ppm loss each day is "normal" ... but that is not true if you are starting at shock levels (in reality you lose a % of the FC every day) ... and every pool is different.

Your use sounds high ... much like I am seeing. With a CYA around 45ppm I am seeing around 5-6 ppm lose each day ... I have a LOT of sun down here so working to raise the CYA a bit more to see if that helps. If you pass the OCLT, that means that most of your losses are sun related.

From Pool School:

If you don't have a SWG or problems from extremely high amounts of sunlight, CYA is typically kept between 30 and 50. If you have a SWG or very high levels of direct sunlight, CYA is typically kept between 70 and 80.

 

[JasonLion]

Chlorine usage is a percentage of your starting level. With CYA a little under 50 you can expect somewhere in the range of 30% to 50% chlorine loss per sunny day in most places, perhaps a bit more or less in more extreme situations.

Once everything is balanced and you are using normal FC levels you can expect to use 2 to 3 ppm of chlorine per day, though again that varies from pool to pool.

 

[ErniesPool]

I should be running close to 4 ppm with a CYA of close to 50. If I lose 50% each day and must replace, it will cost me about $54 per month just in chlorine costs, according to the numbers I am getting from the pool calculator. (I can buy 3 119 oz jugs of 8.5% chlorine at a big box store for $8.50, and if my arithmetic is correct, that comes out to 2.38 cents per oz.). That seems high. But, I don't believe the pool calculator. When I shocked from 0 ppm, I put the calculated amount in the pool to give me 20 ppm. I actually got 33 ppm, so something is wrong. Either my pool is not 25,000 gallons as I was told, or something is wacko.

I just had to pay for almost a whole pool of water because my CYA was too high. That's the second dump in 6 months, so I leery of adding trichlor or dichlor to up the CYA. Anyway, that will increase the amount of chlorine I have to add to the pool to be effective. There must be a discussion about this somewhere on the forum.

I may just experiment with putting in measured trial amounts of bleach and see what levels I get in the pool. I suppose there is a way to back calculate the pool volume doing this.

 

[frustratedpoolmom]

If your FC held overnight for multiple nights, I would suggest trying a slightly higher CYA of 60-70. I know this bucks tradition but if it's clear and you test diligently you can absolutely run with a higher CYA to protect the FC - just don't EVER get lax AND NEVER let the FC drop below your MIN level. EVER.

 

[duraleigh]

But, I don't believe the pool calculator.

Well, it works for thousands of us. What's not to believe?

 

[BoDarville]

But, I don't believe the pool calculator...Either my pool is not 25,000 gallons as I was told...

I believe it's the latter. Pool calculator is spot-on for my pool and seems to be that way for many thousands of us, as duraleigh stated.

I would re-measure the pool volume. There is a tool at the bottom of the pool calculator for measuring pool volume, or you can try this link: Pool Volume Calculator

Other things to check that can contribute to FC consumption include making sure your skimmer baskets and pump strainer are clear of any organic debris. You pool could be spotless, but if there's lots of organic material hiding out in these places, it's still in the system and will result in constant parasitic FC consumption. Same thing goes if you have a pool vac and leave it in the water much of the time. If so, you should clean out the vacuum bag after every or every other use, depending on how much material is in the bag.

 

[ErniesPool]

I measured the pool and it comes in closer to 18,500 gallons not counting the spa, but it's a very rough estimate. My pool is difficult to measure due to its varying dimensions.

There should be a way to do a "dye dilution" test on a pool and get its exact volume, i.e., you put a known quantity of concentrated something in the pool and once it is distributed you measure its concentration. Does someone know how to do this? Measuring a pool's dimensions is subject to big errors due to rounding of the bottom, irregular pool shape, steps in the pool, etc. Also, spa volume.

I should also add that this pool is in Texas, it gets a LOT of sun, and the wind blows fiercely and constantly here, blowing dust and debris into the pool on a regular basis.

 

[jblizzle]

Trust the pool calculator and eventually you will get a better idea of the volume. If you consistently are below or above your targets then you should adjust your volume. It is not that important to be exact.