low pH, high ORP

[Randalli]

For the last week or so my display tank pH has been dropping and ORP is high. The tank is 10+ years old, sand and live rock, sailfin tang, blue hippo tang, 2 black ice clowns, yellow watchman goby and one Randall’s assessor. An orange lip conch, several peppermint shrimp and assorted money cowries, astrea, trochus and cerith snails. There is a large population of hairy green mushrooms, a Kenya tree. Display tank is 6’ long 120 gal with a 40 gal sump. I’m ruuning an ATS on reverse light cycle, skimmer, no media, no dosing. Alk is about 9.5, nitrates have been really high all along (years) >75ppm (!), been trying to bring them down for months with ATS and water changes but not making headway. I feed a small serving of pellets 2x a day and a single cube of frozen mysis once a day. Occasionally a sheet of nori. I have not changed food or salt (Fritz RPM). Temperature is 77-78F, 1.026 SG.
pH is fluctuating from 7.04-7.34, ORP from 430-460.
Not sure what is causing my issues. Water changes are about every 7-10 days and between 10-25%. I have tried a few larger water changes but can’t prepare more than about 25%.

 

[Chris.Reef]

How old are your probes? Have you tried cleaning and calibrating your ph probe? Those numbers seem wrong, ph is really low and orp is very high especially since you didn’t list ozone.

 

[Randalli]

Probes are old but clean. Also recently (last couple months) calibrated with the Neptune solutions. Funny that they both started reporting poor numbers at the same time. Usually my ORP is running 200-300 on the Apex probe.

 

[dz6t]

If your alkalinity is truly at 9.5, pH can’t drop that low. I will say replace the pH probe and the ORP probe. When these probes get old, they can fail quickly even you calibrated them recently.

 

[Randalli]

I probably won’t bother with a replacement ORP probe. They don’t really seem worth the investment. I’ve never been very happy with any of my Neptune probes, especially conductivity, ORP and pH. Thanks for the advice!

 

[Chris.Reef]

Instead of getting the overpriced Neptune probes I would recommend getting a replacement Pinpoint or Milwaukee ph probe, same brands make orp probes as well . These work just fine with the Neptune controller.

 

[Randalli]

Good to know that other mfg probes will work. I checked a sample of my water using a lab grade meter at work which reads my pH at 8.05.