Need a super-low TA on startup to balance pH (and awful test strips too!)

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astrogrl

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Oct 2, 2014
14
Los Alamos, NM
I may have already screwed up this fill- if so, let me know.

This is only the second time I've filled the tub in a house we bought last fall. I had tried Nature2+MPS, but wanted to switch to something that would work at lower temps since we don't use the spa very often. Last weekend, I added SpaFlush, and then drained and refilled the tub. I was under the mistaken impression that the TA had to be between 80-120, so I raised it up to 90 and checked the water balance with my test strips. The Aquacheck7 strips said everything looked great, but the pH was off the charts on my old Nature2 strips. I added 3ppm dichlor while I waited for my Taylor K-2006 kit to arrive. On Tuesday, I brought the FC up to 3 ppm again with dichlor, and did the same on Thursday, so my CYA levels should be something like 8 ppm by now (I've not tested this yet with the kit).

This weekend, I tested using the Taylor drop test kit. Like the Nature2 strips, the pH registered off the charts. I started adding dry acid in about 1oz intervals, with the pumps running about 30min in between each retest. In order for the pH to drop to 7.7-7.8, I've had to lower the TA to 25-30. (I did this once, tried to raise the TA back up to 50-60, but ended up in the same place again to get the pH back down). In the end, I ended up at:

TA = 25-30 (started to change at 2 drops, changed a bit more at 3)
pH = 7.7
CH=140

The Nature 2 strips agree with this, but two different sets of Aquacheck strips (one old, one new), both think the pH is only 6.8. Can strips be off by this much????


My questions:

- Is there a reason my TA has to be so low, or anything I can change to give me balanced water with a TA of >=50?

- Will the necessary TA change as I get my CYA up? I've just supercholorinated to 13ppm.

- According to the Taylor water balance calculator, if my TA is 30, CH is 140, and pH is 7.8, the saturation index is -0.3 at 100deg, and -0.4 at 90deg (where I was hoping to keep the tub when not in regular use). Do I need to worry about the water being corrosive? Should I raise the hardness to something like 200 to compensate?

- I knew test strips could be off a little, but why would they read 6.8 when the pH is really 7.7? Is it possible my pH really is lower than I think, or is the drop test the gold standard? I'm filling to the 44ml line and adding 5 drops of phenol red.

- Did I screw up by not superchlorinating right away? I'm going to check my FC level in the morning to see how much it has dropped. What is an acceptable amount?

Thanks in advance for any insight into all of this!
 
You want TA around 40 to 50. Ideally you want the highest TA that doesn't drive the PH up to much, which is normally around 40 or 50.

You only worry about saturation index in plaster/tile/pebble/quartz tubs. Your tub is presumably fiberglass or acrylic, and if so saturation index can be ignored.
 
JasonLion said:
You want TA around 40 to 50. Ideally you want the highest TA that doesn't drive the PH up to much, which is normally around 40 or 50.

You only worry about saturation index in plaster/tile/pebble/quartz tubs. Your tub is presumably fiberglass or acrylic, and if so saturation index can be ignored.
Click to expand...

That's what I thought, but if my TA is > 30, my pH is >8. If my pH is stable, do I need to worry about the low TA?
 
A few clarifications:

All of the pH measurements were taken before I supercholorinated.

I retested the water this morning, and after 10 hours, the FC had dropped from 13 to 9.5 (27%). Does this suggest that I have a contamination problem from waiting a week to superchlorinate, or is it OK?
 
One more question: The dichlor I added last night had more of an effect on the water than PoolMath predicted- 5tsp should have raised a 358 gallon tub to about 10ppm from zero (which was about where it was), when in fact it raised it to 13ppm. Is the 358 gallon listing in the tub manual the volume when properly filled, or the total volume of the tub (if you were to fill it to overflowing)? If not volume, is there some other reason why it had a larger than calculated effect? The low CYA perhaps?

- - - Updated - - -

JasonLion said:
You want TA around 40 to 50. Ideally you want the highest TA that doesn't drive the PH up to much, which is normally around 40 or 50.

You only worry about saturation index in plaster/tile/pebble/quartz tubs. Your tub is presumably fiberglass or acrylic, and if so saturation index can be ignored.
Click to expand...

Thanks for the feedback- just to clarify, I don't need to worry about corrosion to any metal parts in the pump/heater/etc.? (I'm assuming the water comes into contact with something metal- please correct me if I'm wrong)
 
Low cya would not affect the FC level. It has to be volume or measurement. TA will not affect any metal parts in your tub. Low ph is more likely cause problems than anything else.
 
pooldv said:
Low cya would not affect the FC level. It has to be volume or measurement. TA will not affect any metal parts in your tub. Low ph is more likely cause problems than anything else.
Click to expand...

OK- How low is too low for pH? I checked the tub last night after the jets had been off for about 12 hrs, and it was 7.2-7.3. Running the jets for a bit brought it back up to 7.6. If I understand the spa chemistry correctly, I may be able to raise the TA slightly so that the pH maxes out at around 7.8 when the jets are on, but I'm not sure how much this will change my min pH. I've also not yet added the borates (they are on their way).
 

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