Usually I will see a salt build up if I'm using to much nutes. It happened to me the first time I started growing hydroponically. When I used the Clearex and cut back a lot on the nutes it cleared up and so did the ph fluctuations.
You say the nutes say 1 -2 tsp per gallon, I would go with a 1/4 tsp per gallon at this stage. I would up it to 1/2 tsp during the flowering cycle when fruits start forming. You could go higher if you feel the plants could use more but if the fruit and plants look healthy keep it at 1/2 strength.
Are you checking the ph before or after you add the nutes? It should be checked after. Also make sure your
pH meter is calibrated properly.