ORP, what should you target?

[Gilles]

Yesterday i installed my ORP sensor, and it was reading 172. Today it was reading 163. I've read on the internet various values, ranging from "You should target 300 to 450 for freshwater" and also "You should target 250mv" Can somebody give some explanation about this?

Thank you,
Gilles

[aqua_digital]

I think i should write a book on this subject :)

Ok lets start at the beginning. When you first install a new Redox probe it can take anything up to two weeks to read accurately, the reason for this is because the "ions" have to build up on the platinum electrode.

While this is going on in the first instance the probe value will drop before slowly rising, and the quality of the probe determines how fast this is. For instance I used to years ago import redox probes from the land of the rising sun and the platinum was so impure they would take anything up to a month to reach optimum, but of course with GHL you could be up to speed within days.

Once you see the reading stabilise to a point recalibrate the probe and allow to re-settle, now the probe is fully mature and only needs calibrating once a month and cleaning also.

A sign of a dirty probe is when the reading starts to rise and rise (not fall) at this point do as instructed above.

In regards to readings, well unless you employ ozone to get to the critical level of 450mV it s very difficult to reach this level and anyone that states they have this without ozone i always ask them to clean and recalibrate and then let me know, in most cases the reading falls back to 400 or less. i am not saying it is impossible but very hard to achieve.

So what is ORP reading?, well it is reading the purity of your water, the more pure your water the better ability it has to conduct electricity (mV). But ORP or mV is not an exact science especially when dealing with non ozone environments. It should more taken as a snap shot of the health of your tank.

You will get to know over a two month period the average level your ORP reads, forget for a second what value that is, just take it as an indicator. So for example, you know your system is healthy, you have been good at your water changes everything is doing great and your mV is 300! thats not bad! But you come down in the morning and your mV is sitting at 220mV or worse, this is an "indiciator" something has gone wrong, maybe Nemo pegged it 2 days ago and is nestling in a rock decomposing :eek: So use ORP readings when Ozone is not applied as a refernce to the health of your tank, the reading itself providing it is over 200 as a rule of thumb is not over informative.

ozone is another lesson all together!

[rodouma]

Nice lesson "aqua_digital"!

Just a simple question from me: I just bought a bottle of 220mV buffering solution in order to calibrate my electrode. Can I reuse it for another re-calibration after a month's time? Is it electrically discharged in such a way that it is not 220mV anymore? I understand that the best practice is to throw it away after the first calibration, but I want to know how bad it is to reuse it again (and again)...

[aqua_digital]

Hi

yes you can, best practice is to pour some out into another bottle and put the probe in this, that way you are not cross contaminating.

Regards
Michael