That guy was soooo high when he replied to your question. Whats the connection between a steering wheel and driving fast?

Anyway, I'll try and answer your question about the TDS meter. There are two schools of thought of ppm about whether it should rise every day or fall every day. Until that is resolved what is the importance of the meter? Just follow the directions on the bottles for mixing and watch how your plants react. If your burning them, then back off a bit.

You should change every 7 days. The plants drink well and you want to give them more nutes.