I think it is the nature of nutrient solutions to be acidic. they'll just about always lower your pH, though admittedly, 2.5 points seems like a lot.
I'm not familiar with fox grow, but 2tsp per gallons seems like a lot.

Your tap water is acidic? That's unusual, and - so I've heard - illegal in some countries (corrosion, etc).
Sure that's correct?

Probably well water. Add baking soda in TINY amounts. Like 1/8th tsp, then stir, wait a minute, re-stir and retest. The less you use to get your solution in the 5-6.5 range, the better. Sodium (from baking soda) is not particularly good for plants.

The nutrients are pretty acidic. I see a 2 pH drop from 7 to 5 when I put 2500 ppm of the Flora fertilizer in water (which is substantially more than the recipe on the bottle calls for). It doesn't seem to affect the plants, but 4 probably would.

You could also use lime (CaO). As opposed to baking soda, it would probably be a benefit to your plants since it's free calcium, but I tried it twice and ended up with pH 8.5+. You might have a more steadfast hand though.

if you don't have a steady hand, you could mix a dilute lime mixture. Say 1 cup in 1 gallon. then when you add 1 cup of this mixture, it'd be the same as 1/16 of a cup or 1 Tablespoon.
Just a thought for more control.

thank you for all your help.

i have been using baking soda to bring it back up. used about a 1/4 tsp for 8 gallons to get the ph back up.

what is this lime (CaO) mixture you are talking about? sorry, im a newbie, but trying to learn. sounds like id be better off using that since its good for the plants. thanks!

lime is that white stuff they use to line school football fields. It's high pH, and being made of only calcium and oxygen, quite good for plants. Tricky to use, but grizz's suggestion above is brilliant.

Lime is sold at any garden store, but maybe only in 50 lb sacks. We have low calcium soil here in La, so we go through a bag every year or two. If you have no need for it in your lawn or garden, it'd probably be difficult to justify buying/storing a 50lb sack of it.