Does pH change when covered/with lack of sunlight?

[elsie]

No, it's the right phenol red - I use the AquaChem OTO kit, buying the Aquachem replacement phenol reds as the tube never needs replacing. It's the same kit I used all summer and when I covered the pool. In fact, for this most recent test I used both an almost-empty phenol red and a new replacement phenol red I had not yet opened, and both times the colors were the same, which is an ever-so-pale orange. Clearly, my pH is not high, it must be low. It's just so pale it doesn't begin to match any of the colors on the tube and frankly I don't know how to extrapolate that reading.

The other night I took a water sample and left it outside in the light and retested at night, and got the same result.

The only variables which changed when I covered the pool 2-1/2 weeks ago and now are:

1. Pump is run only an hour a day vs. 24-7 when pool uncovered;
2. Water is devoid of natural light;
3. New cover; and
4. Water sample taken at pump basket instead of directly from pool.

So, the conundrum continues. I guess I should add some Borax?

By the way, early on in the season I happened to be at an Ace Hardware store and bought their brand OTO kit. When I tested the water after uncovering the pool it was a similar weird color. I remembered this happened once before when I bought another brand OTO from Home Depot. So I went back to the AquaChem sold by Walmart (in both cases), and got the correct pink color. I should've brought Ace's back and told them that their OTO test kit could be ruining a lot of liners because it was so inaccurate. At least that was my conclusion - and a very scarey one at that.

[chem geek]

So, the conundrum continues. I guess I should add some Borax?

Yes, you can use 20 Mule Team Borax to raise the pH. If the TA were very low as well, then you could use Arm & Hammer Super Washing Soda (careful: NOT the laundry detergent) instead or some of each depending on how much the TA needs to be raised.