I've had my RA+ since April of last year and I have never been able to rely on my ph probe. I calibrated it with 7/10 calibration fluid and it always read in the 7.7-7.9 range when my ELOS high-range test kit always tested in the 8.2 range. I have tested with various kits and at various times of day and I'm always in the 8.2 range. So I just assumed that my ph probe was off and I would use it to monitor fluctuations in ph.
That was until recently when my probe started reporting drastic drops in ph.. I'd be at 7.8 and then all of a sudden the next day i'm consistently reading at 7.15... Then I get back up in the 7.7 range for a few days/weeks and then all of a sudden back in the low 7's... I have an SPS heavy tank and they are happy with polyp extension so I see no evidence of low ph or ph swings... I also see no way that in an instant my ph could drop that severly, especially when the drop is not consistent with day/night swings...
I really think something is wrong with this ph probe.... could it be affected by any kind of detritus or coraline algae?? I have new 7/10 calibration fluid but I don't want to waste it if the probe is defective...
your assistance is greatly appreciated.
PH probe going crazy
Re: PH probe going crazy
I would start with giving it a good cleaning and then see where it goes. Probes do not last forever. I would give them an 8 month to 1 year lifetime honestly. It's wierd that your getting erratic behavior, which is why I suggested cleaning it first. I usually see "slippage" where the ph slowly gets lower and lower and lower. The other thing to check is having the probe in tank water in an isolated cup of water to eliminate any stray voltage that might be in your tank. I have a similar drop when the probe is in my tank. I'm pretty sure it's from the pump on my skimmer. When I turn that off, the ph goes up .1-.2 so I've adjusted my calibration numbers to compensate. I don't mind a 15-20 minute spike of .2 
vs having my RA display a closer to accurate range. The main point as you said is to monitor for fluctuations. If your pH were 7.15 you'd have no sps left I think...
vs having my RA display a closer to accurate range. The main point as you said is to monitor for fluctuations. If your pH were 7.15 you'd have no sps left I think...Re: PH probe going crazy
8 months - 1 year seems like an incredibly short lifespan for a piece of hardware... Wouldn't there be a warranty that lasts longer than that?
Re: PH probe going crazy
I personally don't consider it just a piece of hardware as there's all kinds of things going on inside. When my last RA probe was giving me issues, I ordered a pinpoint probe and it lasted me about 8 months before I started seeing it slip. This time I'm trying the lab grade probes.. let's see..