Good Calcium hardness number?

Reading another tread it stated to keep calcium between 200 - 400. I do have some spots of pitting in my plaster. The pool is 10 years old and I don't think the previous owner ever tested for CH. I raised it some when we moved in, it is now 180ppm.

results from this mornings test:
Ph 7.2
TA 110
CH 180
CYA 60
CL 4.5
CC 0

I started another tread in the Cl` section that should probably be here, I was asking about raising my borate levels up to get the Ph up. Do not have a borate test kit/strips yet.

Could it be possible the pitting is due to years of low CH? The pits are kind of discolored compared to the other parts of the plaster.

Quote:

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Originally Posted by lstinthot

Reading another tread it stated to keep calcium between 200 - 400. I do have some spots of pitting in my plaster. The pool is 10 years old and I don't think the previous owner ever tested for CH. I raised it some when we moved in, it is now 180ppm.

results from this mornings test:
Ph 7.2
TA 110
CH 180
CYA 60
CL 4.5
CC 0

I started another tread in the Cl` section that should probably be here, I was asking about raising my boate levels up to get the Ph up. Do not have a borate test kit/strips yet.

Could it be possible the pitting is due to years of low CH? The pits are kind of discolored compared to the other parts of the plaster.

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First the borates:
You do not need a test kit if you are using borax to raise pH. You need a pH test! You use just like pH increaser at twice the amont by weight.
This means use about half a box for each 10k gallons, wait a day, and test pH. If it is still too low repeat. Pretty easy.

The pitting is caused by unbalance water. Low calcium is a part of that. pH is a very important part of that and low pH was probably a common problem since I am going to assume the previous owners used trichlor and only tested TC and pH (pretty common) and did not monitor TA and it dropped along with the ph many times. Combined with low calcium you have a recipe for pitting plaster. Right now your water is a bit on the aggressive side (saturation index of -.45 assuming a water temp of 76 degrees) , but otherwisey it is fine . Saturation index should be between .6 and -.6 (Some say .3 to -.3 however).

I would suggest getting the pH up to 7.6 and your water will be balanced perfectly (saturation index -.07). If you find that your pH is constantly rising too fast (because of the high TA) then you can lower the TA to 80 ppm, and raise the CH to 300 ppm after the TA has been lowered and you will still have balanced water at pH 7.6 (saturation index of -.06). However, if the pH stays stable then don't fix what ain't broke. As a general rule you want to keep the CH between 200-400 and the TA between 80-100 for a plaster pool running bleach or other unstabilized chlorine.

The two factors that have the BIGGEST influence on whether the water will be aggressive to plaster or not are not calcium and TA but rather pH and temperature in that order. Since temperature is often out of our control them the best way to prevent plaster damage is to keep the CH and TA in the recommended range (and don't lose a lot of sleep over the exact numbers as long as it's in range) and keep the pH between 7.5-7.8.

Normally I am fighting a pH that is lowering. Just tested this morning pH is 7.4 and FC = 4ppm CC = <.5. Did the .5ppm per drop and it was just slightly pink after I added the stuff to test for CC. I figured I was on the aggressive side, that is what made me start looking into the borax and how much to add. Thank you for the help.

Quote:

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Originally Posted by lstinthot

Normally I am fighting a pH that is lowering.

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Are you by any chance using tabs in a feeder or floater? Normal tendency for a pool with a TA of 110 ppm would be rising pH unless a stabilized form of chlorine (trichlor tabs or dichlor), or other acidic oxidiers (MPS-non chlorine shock or bromine tablets) are being used. If you are using bleach or liquid chloirne (sodium hypochlorite), cal hypo (calcium hypochlorite), or lithium hypochlorite for your chlorine source then you would see a rising pH.

I am only using bleach now. About 1.5 gals per day and keeps FC around 4 when I check it in the morning. I add at night before the pump is turned off. I am working nights so my kid is adding while I am at work so I am not sure what level the FC gets to at night. Not sure of the drop over night. At this rate it is going to cost us about $100/month for chemicals. We are starting to get a lot of leaves in the water, Polaris is cleaning them up during the day. Pump only runs one cycle due to pump not maintaining prime, I have to babysit it till it gets going. We run it during the day so if the power goes out or something happens we can help it get back started. We look into fixing the priming issue wants work slows down.

The chlorine costs are on the high side due to the pool being large at 36,000 gallons. Not much you can do about that except possibly getting a mostly opaque cover since most of the chlorine loss is from sunlight.

We keep the solar cover on all the time except when the kids are swimming. Not sure how much more swimming they will be doing this year, temps at night are getting in the 40s. Pool is still staying pretty warm, not sure for how much longer.