ORP and new salt water

[Ebslinger]

I see a large drop in ORP following a water change.

Question: Is it caused by a sealed container?

Back ground: I currently mix up about a months worth of salt water (for water changes) at a time. I am using tropic marin pro reef mix and RO/DI water. The mixture is stored in a brute trash can with lid. Seem to be fairly tight fighting with power-head and heater cords.

Anyway, I do a water change and see a 90 point drop. About 30 points right away, and then a continued drop over the next several days for a total of about 90.

Any Ideas?

I have seen several similar posts, but nothing that really addresses this issue.

Thank you for your time!

 

[Jay Z]

Normal. My orp for my ozone is set at 400. Drops to 350 when the awc kicks on. That’s only a gallon change.

Don’t mind my apex value. That probe never works right when the ozone’s on. It’s 75 points over my Milwaukee’s on a good day. But every drop is when my awc kicked on. 3 time a day.

 

[Ebslinger]

@Jay Z Thank you for the reply!

While you said it's normal, I guess I wonder why it's normal... what is causing the drop in ORP?

In my mind, I see ORP readings related to dissolve oxygen... is that wrong?

 

[Jay Z]

My best guess when new water is added the tank starts to manipulate it into tank water. The process take a small toll on the tank orp until it levels back out. Just like when contaminated water is introduced the skimmer goes on over time.

That my guess on it. I’m not good at adding words or spelling numbers.

I’m not a orp pro. But we do have one here in our community. I’m sure he will chime in and set the record straight.

 

[lapin]

Officially it is a way to measure water's ability to either release or accept electrons during a chemical reaction. When i dose a cloud of reef roids, phyto and oyster feast the ORP drops.
So to me the probe measures the ability of the water to absorb oxygen.

 

[Ebslinger]

Ok, lets assume we need oxygen to be present for oxidation to occur.

Can a semi sealed container of saltwater consume the available oxygen and there by lower it's ORP ?

 

[Randy Holmes-Farley Verified Community Expert]

I see a large drop in ORP following a water change.

Question: Is it caused by a sealed container?

Back ground: I currently mix up about a months worth of salt water (for water changes) at a time. I am using tropic marin pro reef mix and RO/DI water. The mixture is stored in a brute trash can with lid. Seem to be fairly tight fighting with power-head and heater cords.

Anyway, I do a water change and see a 90 point drop. About 30 points right away, and then a continued drop over the next several days for a total of about 90.

Any Ideas?

I have seen several similar posts, but nothing that really addresses this issue.

Thank you for your time!

It is caused by the relative amount of trace metals like iron in reduced forms (ferrous) vs oxidized (ferric) forms. It is no concern, and clearly demonstrates that ORP is not a suitable gauge of cleanliness.

 

[Randy Holmes-Farley Verified Community Expert]

Ok, lets assume we need oxygen to be present for oxidation to occur.

Can a semi sealed container of saltwater consume the available oxygen and there by lower it's ORP ?

Some sort of reducing agent would need to be added, but that is not typically why salt mixes often have lower ORP to begin with. It's just the types of ingredients used. Ferrous iron (low ORP) is much more soluble then ferric (higher ORP), for example, and is likely the one used by most manufacturers.

 

[Randy Holmes-Farley Verified Community Expert]

@Jay Z Thank you for the reply!

While you said it's normal, I guess I wonder why it's normal... what is causing the drop in ORP?

In my mind, I see ORP readings related to dissolve oxygen... is that wrong?

Correct,, that is wrong. lol

Simply put, the new salt water has lower ORP than the tank. It is not related to dissolved oxygen.

 

[Ebslinger]

@Randy Holmes-Farley Thank you for taking the time to reply. I quess I need to go back and re-read your ORP article. Maybe even crack open some of those college chemistry books that have been sitting in the garage for 30 years...lol

 

[Randy Holmes-Farley Verified Community Expert]

@Randy Holmes-Farley Thank you for taking the time to reply. I quess I need to go back and re-read your ORP article. Maybe even crack open some of those college chemistry books that have been sitting in the garage for 30 years...lol

You're welcome.

Happy Reefing.