Does dry acid vary somewhat in its strength? I used the pool school calculator to determine how much dry acid I needed to bring my pool down from 8.0 to 7.5. I used a scale to measure by weight, added it to the pool last night, and measured my pH again today. It looks to be about 7.2. Is it unusual to get a result off by that much?
Dry Acid
- Thread starter frogkick
- Start date
The main body of the pool is 14 x 30 rectangle with a 4'-5'-4' sports bottom. In addition to that 14 x 30, there is a seating area and stairs, which I can't imagine add that much so I didn't bother with the math on those. I'm getting just over 14k gallon for that main pool body. Am I doing the calculation wrong?
It is better to use muriatic acid because dry acid scosts more and adds sulfates. Sulfates will build up and damage metal and concrete surfaces.
Ph calculations are approximate and vary based on TA and other factors. It is best to undershoot pH adjustments a bit. Which is why PoolMath has this note:
Ph calculations are approximate and vary based on TA and other factors. It is best to undershoot pH adjustments a bit. Which is why PoolMath has this note:
Are you sure your gallons are correct?
The other thing I always like to do is break my doses up.
If it says add 4. I start with 1/2 to 2/3 of the recommended dose. Let it circulate 4 to 8 hours and retest.
I'd rather work my way up or down slowly rather than overshoot and have to adjust in other direction.
PoolMath is invaluable but it's entirely dependent on all of the parameters.
Does your pool have exactly 11k gallon of water in it now? In a 15x30 pool 1 inch of water ~ 280 gallons. I don't know about you but I have no way of now exactly the amount of water in my pool at any given time.
When I do a 10 ml FC test and it goes to colorless on drop 6. Do I have exactly 3 ppm? Very unlikley
TA test - at the 8th drop amy I exactly at 80? Very Unlikely
PH read 8.0. Is it exactly 8? Very Unlikely
CYA - I read 60 but is it exactly 60. Not likely.
1. Test kits have a margin of error and are only generally correct. A kit dropper and test tube are not even remotely accurate in scientific terms.
2. Maybe you squeezed a little hard and got more agent in the tube or less agent.
3. Maybe you only had 9.90 ml vs exactly 10 ml
4. Maybe your starting PH was closer to 7.8 than 8.0. I know my Taylor 2006a only has 7.0, 7.2, 7.4, 7.6, 7.8 and 8.0 measurements. The one thing I don't know for 100% is how gradually the colors change as the PH changes.
5. Maybe your scale is not 100% accurate.
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I hear you on this one. But what is one to do with 75lbs of Dry Acid they purchased before finding this site?
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Maybe. What are you using for Average depth?
4.25 to 4.5 is 600+ gal.
cfherrman
TFP Guide
Using 4.5' as the average depth. The pool seems to run a little deeper in general, if that makes sense. I guess it's an approximate depth with gunite and it came out a few inches deeper all around than I had expected. I can see if the other calculations overshoot my target too to decide if I'm overestimating the amount of water in the pool or if it's something specific to the pH. Good thing I aimed for the middle. 
Weeeelllll.....on the bright side, it's only a 10 lb bucket of dry acid so I should be able to use that up, I assume. On the other hand, I've been using pucks to raise my CYA because I have a ton of them and I'll surely have more puck than CYA need. Once I get my CYA where I want it, where the heck do you dispose of chlorine tabs?
Weeeelllll.....on the bright side, it's only a 10 lb bucket of dry acid so I should be able to use that up, I assume. On the other hand, I've been using pucks to raise my CYA because I have a ton of them and I'll surely have more puck than CYA need. Once I get my CYA where I want it, where the heck do you dispose of chlorine tabs?