What is ORP/Redox?

[Philosophos]

Tom, I'm asking this one from you specifically, because I don't trust anyone else to explain it to me. I've never tried so hard to understand a topic in fish keeping and been so stumped. Google cackles at me, and hobbyist articles seem to have all the credibility and detail of homeopathy.

The salt water guys at the LFS tell me it's the only number that matters, but not why.

Should I start scrying with some chicken entrails, and hope that the ORP fairy gives me a favorable number?

I've taken the time to do some A1 Chem reading once again, and my understanding is still shaky.

A little help please?

-Philosophos

 

[Tom Barr]

Chem 101 is a good starter.

This gives a good run down of the basics:

Redox - Wikipedia, the free encyclopedia

This tells you what you need to know for the most part for the basics in our case(view slides 2-6 or so):

http://kearney.ucdavis.edu/Undergrad_Fellowship_Reports/ChangKearney_Presentation.pdf


You understand both of these, you'll know more than 99% of the aquarium hobbyists, maybe 99.9%.

Regards,
Tom Barr

 

[Philosophos]

Sounds like I've got work to do then. I have the PDF saved, and I'll give it a read over. I'll keep reading it over and trying to figure it out until I've got this down.

Thanks for the links, Tom.

-Philosophos

 

[cggorman]

If you haven't, you might want to check this article out: How Aquarium Redox Balance, Potential, & Reduction relates to aquatic health

it has a more narrative style that was easier for me to understand in practical terms.

 

[Philosophos]

Thanks for the link cggorman; i had come across that one a few months ago, but had forgotten about it.

The light is starting to turn on for me, but the application seems pretty big and complex. It looks like I'll be re-learning the ORP side of all aquarium chemistry.

I think I've been wondering about things that would be covered by ORP for a while now. Pure pH reading never seemed to quite answer buffering questions.

-Philosophos

 

[Tom Barr]

In context of planted tanks, ORP is 100% in the sediment when it come sot processing.

See that slide in the pdf ppt presentation where the lower grades of reduction occur the lower the Redox becomes(more negative).

We tend to have the NO3/Fe range, not the H2S range(sulfide reduction).

All the gas bubbles coming out of the sediment is mostly aerobic and CO2........not H2S or CH4 etc in our tanks.

Regards,
Tom Barr

 

[Philosophos]

Tom, you just straightened me out on a big question I've had, and left me with another.

The NO3 reduction bit was the answer. The question it raises is where does all the sulpher go? The ferts that I mix up are pretty SO4 heavy, and I some how doubt the plants are consuming it all. Do substrates turn into toxic sulpher sinks after a while?

-Philosophos

 

[Tom Barr]

SO4 is removed via plants, filter cleanings and the water changes.

Regards,
Tom Barr