A question from a fellow grower:
can i lower pH with lemon acid (C6H8O7). Will that acid destroy plant?
Lemon juice can work just fine as a pH down in many cases.
The issue with using Lemon juice is not that it would be detrimental to the plant, but the likely possibility that it will not maintain a consistent PH in the reservoir. You do not want to get into a regimen of having to provide acid to your reservoir to often.