Adding borates - how much can it slow pH rise, and effect on MA/TA relationship.

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lalittle

Well-known member
Apr 4, 2011
184
Los Angeles, CA
I noticed in the Pool Calculator that when borates are added to a pool, the amount of muriatic acid needed to lower the pH by a specific amount goes way up (more than doubles even with borates at 40ppm.) I"m curious if the effect of the acid on TA changes as well -- i.e. do you still get the same amount of TA drop from MA that you did before adding borates?

I'm considering adding borates in order to slow the significant pH rise in my pool, but given that my TA tends to steadily drop to 40 or so due to my twice-a-week acid additions, I'm wondering what will happen with regard to the longer term effects on TA drop after adding borates. Will the pH rise slow down enough to completely compensate for the higher amount of acid needed to raise it? Or, will I end up having to chase the dragon trying to keep the TA up to a reasonable level while adding higher acid doses at a slower interval?

I guess the information I'm looking for is some idea of how much effect on pH rise to expect from the borates. I know that this will vary from pool to pool, and that there are factors in play that there aren't any solid numbers for (such as how fast the pH actually rises), but I'm looking for general guidance here. For example, does adding 50ppm borates approximately "halve" the pH rise, or does it do more (or less) than this typically? If I halve the pH rise, but need to add twice as much MA half as often, I haven't changed things all that much.

Thanks,

Larry
 
If you don't change anything else other than adding borates you will need to add twice as much acid half as often, i.e. the same total amount, and raise TA just as often as before.

The big advantage of adding borates in a situation like yours is that you can lower the TA, which will slow down the PH increase and reduce the total amount of acid needed. Without borates we don't recommend lowering TA below 60. With borates you can let TA go down to 40 or 50.
 
Okay -- so adding borates does cut the pH rise by about half? Is that a "maximum" -- i.e. does that happen at 50ppm borates (as opposed to 30 or 40)?

Does the relationship between pH rise speed and increased MA demand stay the same when adding borates? In other words, if I add enough borates to exactly halve the pH rise, will I need exactly double the MA to cause a 0.2 rise in pH (compared to the MA needed for this without borates)? It sounds like you're saying that the change in pH rise after adding borates tracks linearly with the increased MA needed to cause an equivalent rise.

Is it at all possible that the borates will slow the pH rise by more than half, and that my overall acid demand will drop?

Thanks again.
 
The wording gets complicated to keep straight. Once you add borates, the rate of PH increase slows down, but it takes more acid to bring it back down, so the total amount of acid stays the same (assuming you don't change anything else).

If you are concerned with the total amount of acid used, you need to lower TA. Lower TA means less PH increase and less total acid used. However, you can only lower TA so far, and you can lower TA further when using borates
 
I always thought the borates could help to "lock in" the pH level -- i.e. actually keep the pH from rising. My understanding now is that borates simply slow down the change -- i.e. if you have pH rise, you'll STILL have pH rise with borates, but it will just be slower. Is this correct? I understand the idea of allowing for lower TA, and therefore slower pH rise, but in my pool I don't notice a significant difference in the speed of pH rise when my TA is lower. The speed of pH rise seems the same at a TA of 90 as it does at a TA of 40. Note that unless I keep adding Baking Soda to bring the TA up, my TA always drops to around 40.

Does the actual cause of the pH rise have any bearing on this? In other words, does the effect of borates on pH rise change depending on exactly what the cause of the pH rise is?

Thanks again,

Larry
 
Borates have the same effect, regardless of the source of the PH increases. TA has different effects depending on the source of the PH increase, i.e. sometimes high TA is what is causing your PH increase, and other times something unrelated (like fresh plaster, etc) is causing your PH increase.
 
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