Low ORP reading

[hypnoj]

I just purchased a new ORP probe for my SPS tank and hooked it up to my reefkeeper last night. Once the probe was placed in my sump my ORP started out at around 220 and then slowly lowered to 157 by around 10 pm. Everything I've read states that this level is extremely low.
A little bit about my system:
80 g SPS rimless open top cube, GAC/GFO reactor, ATO with kalk/vinegar/NOPOX
small refugium area in sump (where probe is located).
I dose Red Sea reef Energy A & B twice a week, each of the Red Sea coral colors once a week.
Very heavy fish load. (fish fed once a day with ocean nutrition dried food)
I do weekly water changes of 5 gallons each.
salinity 1.024
pH 8.10
Nitrates 0
PO4 0.05
Ca 460
Alk 7.7
Mg 1460
In general the tank is beautiful but seems to be growing fairly slow the last few weeks.
Please lend me your comments or ask any other questions you might have.

[disc1]

Have you calibrated the meter with that probe?

Generally with ORP the absolute numbers don't matter much. You should be looking for trends around the numbers that seem normal for your tank. If you're not running ozone, ORP reading are pretty useless. But occasionally you can learn something from the trends.

[hypnoj]

I got it just for trends, even though I may run ozone at some point. I don't know how to calibrate the meter to the probe, so it looks like I'll have to do some digging to find out how.

[disc1]

I got it just for trends, even though I may run ozone at some point. I don't know how to calibrate the meter to the probe, so it looks like I'll have to do some digging to find out how.

If it is a new probe and you haven't calibrated it then you can't say anything about that number. You might as well have just picked a number at random.

[ca1ore]

Also, ORP probes can take a week or two to 'break in'.