There are some in the base nutes, and that should more than make up for the baseline of 250ppm. I only have to add about 15ml to 5 gallons to get close to 250 and then I add my nutes. I never go full strength on anything, but I will go 85% from the last week of veg till the 6th week of flower.( about 7 weeks or so). I do recommend finding out if your water company uses chlorine or chloramine. If you can't, I would recommend a chlorine/chloramine remover and use it before you use the water for the plants. My base ppm is 170-180 and after I add the chlorine remover, it goes up to 200-210ppm.
The difference in the smell of the water is night and day when I use the treatment. Chlorine tends to be tough on most root microorganisms, so the products that work on or in the root zone will be better off if you make sure it is gone. Chlorine also makes plants brittle, they will look fine, but will lose a lot of there elasticity in the cell walls from what I have read and observed in my first grow. I let my water set for at least 4 days, then add the treatment and aerate it for a couple of hours before I add nutes.
Hope this helps.
Peace and Great Grows
Asmallvoice