My CYA & CH levels doesn't match The Pool Calculator

[ChiknNutz]

I clearly MUST be doing something wrong, but here are my calculations AND test results to back it up.

Sundance Altamar spa: approx. fill volume is 385 gallons (total capacity of 455) per manual and everything I've read so far. All numbers are based on 385 gallons.

Based on that, 2.9 oz. of Dichlor SHOULD raise my CYA to 28 ppm (per The Pool Calculator). I added that much dichlor over about 4 days, with the last application of 1/2 ounce on 5/24. Since then I've used just normal 6% bleach per BBB method. Everything else is in spec. I just tested my CYA today (using TF-100) and my CYA barely registers...so it's less than 20. Meaning, the black dot is still visible even with the tube completely full (slightly obscured, but still visible).

Further, I added 4.6 ounces of Calcium Chloride (Leisure Time liquid Calcium Booster), which should have raised my CH level from fresh fill CH of 50 to desired CH of 150. I tested CH today as well and CH is at just 80.

So, please tell me where I have gone wrong so far. :?

 

[JamesW]

Some dichlor is less than pure dichlor. Check the ingredients on the label to see how much actual dichlor the product contains.

The liquid calcium will not be pure calcium chloride. Check the ingredients on the label to see how much actual calcium chloride the product contains.

 

[ChiknNutz]

The dichlor claims to be 99%.

The liquid does not list the actual ingredients.

 

[JasonLion]

The CYA test is +-15, so you are within the tolerance of the test. None of your numbers are exact, pool volume, amount of chemical added, test results are all going to be off by 10% or more, so you will only get a good agreement with calculations if you are very lucky.

 

[ChiknNutz]

So for my CYA test, should I go by what the Pool Calc says based on how much Dichlor I've added OR go by the test? I would think the calculations should be more accurate. I added another 1/2 ounce of dichlor last night cuz I thought something was off, so now, by my calculations, the CYA should be about 35. I am very careful when adding the chemicals, so I am certain of how much I've added. The only thing that might be subject is the spa volume. I messed around with the Pool Calc using a range of water volumes and though the chemical amounts do vary some, not really too much...less than 5% deviation.

 

[JasonLion]

If you have test results, go by the test results. If you don't have test results, go by your calculations.

If the test results and the calculations differ by more than the precision of the test then there are several things to investigate: are the test reagents still good, are you doing the test correctly, is the chemical you are adding still good, are you measuring correctly, and so on.