Hi jtrain
I'm not sure how to add to your reservior. I make up a solution in a separate bucket all together and add nutrients then additives all in proportion to how much water I'm replacing. Then ph to a level that will correct my current ph. I can't get hydroguard in Scotland so I'm using cannazyme I put it in every time I top up only the amount stated for the volume getting topped up. Hope this makes sense! Just add a little more nutes to get ppm up do it in small increments like .5 ml and mix and test. If you are not sure have a look about the forum I usually spend a good while reading the stickies before I do anything.
Wynnyin