Originally Posted by
dspeers
So basically your ph swing was due to an accumulation of CO2 when dark rather than exuberant photosynthesis raising your ph during the day. If you are satisfied with plant growth then the first problem can be addressed by increasing the effective water surface area. Had it been the second issue, would have either required adding CO2 during the day or keeping the plant biomass way down as you have already done. My understanding of the negative effects of alkaline water on plant growth is that several important nutrients, Iron, Calcium, etc. become less soluble as ph goes up causing deficiencies.