Strange EC issue DWC last few weeks of flower

[KnuckleHead]

I have 2 plants going (cement shoes and amnesia haze) in individual DWC buckets. I am in week 9 of flower. I have an auto feed water system I made so that they are always topped off with fresh water as they drink. In these last couple weeks of flower I am running .8 EC, of which .4 of that is the tap water.

Water change day is every saturday. Saturday they got their fresh nutes, sunday ppms on both went down from about 400 to 380, and ph edged up. I'm liking that. Monday same thing, Tuesday the EC spiked over 100 ppms in both buckets to 500 and ph tanked to 4.0. I repaired all that yesterday by watering down the nutes and put the girls to bed with 6.0ish ph and got the ppms to 430. Today they both went up about 50ppms and ph went down to about 4.5. So about half as severe. I've watered down the nutes again cuz it's all I can think to do. I'll see how they are tomorrow.

Anyone have any ideas what this behavior means? I'm wondering if they liked the fresh nutes for the first few days, but took the certain nutes they needed and don't need whatever is left. I almost want to change the nute water again to see what happens.

 

[Smokey0418]

Not sure what’s in your .4 water could be something useful and not.

So I personally would be trying about 1.1-1.2 ec on top of your questionable water , so 1.5-1.6 then tapering off to .8 near your end or 1.2 in your case.

I find not having enough nutes in my water makes it difficult to control ph.

 

[Zill]

Measuring pH accurately is difficult if salts are lacking. way too much drifting between two readings. Not necessarily hard to control. Hard to measure.