Ph meter issue with submersible water pump

So I'm running a 4 site rdwc with a submersible water pump running waterfalls to each site from the res. I have 3 different cheap ph pens (not ready to bite the bullet on an expensive one yet). When I try to test my ph in my res I get errors and misreadings, however if I drop that same meter into a plant site bucket I can get actual readings with no issue at all.

I'm wondering if anyone has run into this issue or could speculate on what's going on. I also have a tds meter that takes readings just fine in my res bucket, so I dont see this being an issue with an exposed/loose wire to my pump. I'm kinda confused and I dont wanna have to lift plants from their sites (especially late in flower) to check my ph.

Should i bite the bullet on a top shelf ph meter and hope it helps? I know Amazon has great return policies.

Pull a sample from the res and read that with your meter.

A shot glass works great, one with a heavy bottom and the pen will stand there while it sits on a table.

Renfro said:

Pull a sample from the res and read that with your meter.

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Why tf didnt I think of that. Guess I forgot about KISS. Thanks man!