Borate application, redux

[waterbear]

(this was originally posted as an answer, here: http://www.poolforum.com/pf2/showthread.php?14386 , but moved to the CS by me for discussion -PoolDoc)

I am going to assume you have a 5000 gal pool with attached spillover spa (mine is only slightly larger at 6500 gallons for the pool and 300 for the spa) and when you want to use the spa yo isolate it from the pool by turning valves but it is normally one body of water.
I also assume that the total gallons for both pool and spa is 5000,

I am going to give slightly different instructions for the borax and acid then PoolDoc did.
1. First, order some LaMotte borate test strips (easier to read than the AquaChek strips).
2. Next have a small kitchen scale handy since you will need to weigh out the borax.
3. For ever 1000 gallons you will need 60 oz by weight of borax and 30 oz by volume of 20 baum muriatic acid to go from 0 ppm to 50 ppm (to make things a bit easier call it 4 lbs of borax and a quart of acid. It will be easier to measure and close enough for government work since you will make final pH adjustments at the end and the borax does not to be at exactly 50 ppm.). Remember each box of borax is 4.75 lbs and NOT 4lbs.
So for 5000 gallon you will need 20 lbs of borax (4 boxes is 19 lbs..close enough)
You will also need 5 quarts of acid ( 1 gallon and 1 quart). It might initially have the pH a bit lower than 7.6 but it will rise on it's own so it's not a worry.

Before you add the borax get your TA adjusted down to 70 ppm and make sure your CYA is at the manufacturer's recommended maxiimum for your SWCG, ususally 80 to 100 ppm--80 for Intellichlor (both of these will help slow pH rise for reasons to lengthy to go into now.) You did order the K-2006 , right?

4. adjust pH to about 7.6
5. you are now ready to add the borax. Turn on pump. Dump half the amount of borax directly in the pool and then add half the acid by either diluting it in a bucket of pool water a quart at a time or by pouring it SLOWLY into the stream of a return that is not near the skimmer.
6. brush down the sides of the pool to mix everything
7. add the rest of the borax and acid in the same way, brush again.
8.circulate for the next 24 to 48 hours then retest borate level, pH, and TA. Borate should be 50 ppm or slightly above, TA should be holding at around 70 or 80 ppm and pH should be around 7.6 yo 7.8. If it is lower don't worry, it will rise by itself (as long as it is above 7.0)
If it is higher use your acid demand test to determine how much acid will bring it down to 7.6.
Your pH should now stabilize around 7.7 for an extended period of time. When the pH climbs above 7.8 add acid to bring it down to 7.6 but not lower (since the lower you put the pH the faster it will rise) The acid demand test in the K-2006 will help you at first to learn how much acid you will need but afte a while you will be able to 'eyeball it' and hit it pretty close.

When your borate drops to 30 ppm (from backwashing, splashout, etc.) bump it back up to 50 ppm. 12 oz of borax by weight and 6 oz of acid by volume will raise 1000 gallon 10 ppm.

It's really MUCH easier than it reads and it will help stabilize the pH in a salt pool. The main cause of your pH rise is outgassing of CO2. Lower TA means less carbonation in the water means slower outgassing means slower pH rise. Maximium CYA means less cell on time means less hydrogen bubble generation means less aeration of the water means less ougassing of CO2 means slower pH rise.

Borates introduce a secondary buffer into the water (and have other benefits such as their algaestatic properites) which works to lower pH while the primary bicarbonate buffer works to raise pH. Together they make the pH stay around 7.7 for a longer time than without borate in the water.

Hope this helps.