Different PH readings

So I'm running my first coco grow. I've got 70/30 coco/perlite mix and went with lucas formula for a feeding schedule on some autos.

Im having an issue getting different ph readings when I measure the ph of the water in the reservoir vs measuring the same water's ph in a smaller measuring beaker. Both the res and the beaker give me consistent readings everytime, they're just different... it's the same water, but why do I get different readings based on the volume of water?

Which measurement should I go with? Is this normal? I've got a 2nd large res that I let the tap water dechlorinate in and get the same reading each time in that one, no problem. So I dont think its the ph pen not working properly. It's been calibrated recently as well.

Water out of the tap is 200ppm w a ph of 9.3

Decholorinating Res ph =9.3
Nutes in Res ph=10.1
Nutes in Measuring Beaker ph=6.1

Plants look good except for 2 showing some lockout or nute burn bc I just realized the issue with the ph readings so there was some ph swing. If something was seriously wrong, I think I would see issues w more than 2 plants....right? Unless these are the first 2 plants to show and maybe I could be eeing more hurting soon.


Thoughts? Why does the water ph levels read differently when I test it in the reservoir versus in a measuring beaker?

your ph should go down after adding your nutes,at least mine do.why your getting different readings ihnc thats just wrong.mix some baking soda with water ph should be 7.9.

The ph does go down when I add nutes. I mix nutes in a 5 gallon bucket then ph the solution and top off the res with that.

When I stick the ph meter in the reservoir it reads 10.1, however when I scoop up a sample of the water with the beaker... then it reads 6.0 when I stick the ph pen in the beaker. Same water, 2 different readings depending on the size of the volume of water. So weird

I dont empty and clean the res but every 2 weeks. It's a 13 gallon fliptop trashcan reservoir (it was brand new when I started using it lol)

Idk... Maybe it's time to clean the res

pH drops are worth their weight in gold, and inexpensive. Perhaps you can get some and double check what you're seeing. Never the less, a pH of 10 is no bueno, and a swing of 4 whole points is enough to leave you scratching your head. Good luck friend.

dechlorinated water with pH of over 9 is brutal. and you're saying it'll still go more alkaline up after adding nutes? what are these for nutes? good food for canna should actually make the pH drop.

sounds like your pen is trash. if it is, it wont also calibrate justly...

Just spitballing hear. Do you have anything electrical your res? Pump? May be leaking some voltage. I would use the beaker reading. And quality of your pen may be a factor.

Water thats moving will often read differently than still water. I have to pull a sample from my nute tanks because the oxygenation and movement throws the reading off. Some meters are more prone to this like my Apera. Bluelabs don't seem to have the issue.

Change the battery in your ph pen then calibrate or get a new ph pen.