Mike's fish room musings

[Wookii]

In laymans and practical terms is ORP reduced by organics in the water column, and increases by dissolved oxygens in the water column, or are there other factors within an aquarists control that can affect ORP?

So what would be the 'ideal' ORP measurement for an aquarium? I don't have an ORP meter, but what would be the ORP of clean but fully oxygen saturated fresh water?

 

[MichaelJ]

In laymans and practical terms is ORP reduced by organics in the water column, and increases by dissolved oxygens in the water column, or are there other factors within an aquarists control that can affect ORP?

Very good question!

So what would be the 'ideal' ORP measurement for an aquarium?

Thats sort of what I am hunting for as well! If > 320 mV may hurt invertebrates that sort sets the upper limit for me.

What can we do if the ORP gets too high or too low? Too low might be the easier one to deal with as it seems to correlate with waste buildup, lack of filtration (dissolved organics) etc.

Cheers,
Michael

 

[dw1305]

Hi all,

I'll see what I can find.*

Not a lot so far.

cheers Darrel

 

[Wookii]

What can we do if the ORP gets too high or too low?

Yeah too low is the easy one - change some water and have a clean up presumably.

Too high - I'm not sure if that's possible in an aquarium unless you inject O2. That's why I asked what the ORP measurement was on a saturated fresh water sample, as that should be the theoretical maximum.

 

[dw1305]

Hi all,

So what would be the 'ideal' ORP measurement for an aquarium? I don't have an ORP meter, but what would be the ORP of clean but fully oxygen saturated fresh water?

Saturated would always be all right, the issues would come with "supersaturated".

I'm going to say anything above 400 mV is going to be an issue. This <"was ~200% oxygen saturation"> and that had done for several of the Goldfish. Unfortunately I don't know what the ORP value was.

....... I had an interesting one today. I won't tell you the location, or context, but it was a pond and the water sample had a dissolved oxygen level of 180% (~20oC, 18mg/L DO) and a pH value of pH 10.5.........

In <"Marcel's article"> he gets to more than 440 mV without any apparent damage to Amano Shrimps.

This is from Stiller, K.T.; Kolarevic, J.; Lazado, C.C.; Gerwins, J.; Good, C.; Summerfelt, S.T.; Mota, V.C.; Espmark, Å.M.O (2020). "The Effects of Ozone on Atlantic Salmon Post-Smolt in Brackish Water—Establishing Welfare Indicators and Thresholds". Int. J. Mol. Sci. , 21, 5109. <"The Effects of Ozone on Atlantic Salmon Post-Smolt in Brackish Water—Establishing Welfare Indicators and Thresholds">

....... Salmon were exposed to oxidation reduction potential concentrations of 250 mV (control), 280 mV (low), 350 mV (medium), 425 mV (high) and 500 mV (very high). The physiological impacts of ozone were characterized by blood biochemical profiling, histopathologic examination and gene expression analysis in skin and gills. Fish exposed to 425 mV and higher showed ≥33% cumulative mortality in less than 10 days. No significant mortalities were recorded in the remaining groups. ........

cheers Darrel

 

[jaypeecee]

In laymans and practical terms is ORP reduced by organics in the water column, and increases by dissolved oxygens in the water column, or are there other factors within an aquarists control that can affect ORP?

Hi @Wookii & Everyone,

Yes, the presence of dissolved organics lowers the ORP value and that's why it is used to gauge the level of water pollution.

I find that addition of Seachem Iron (ferrous gluconate) lowers the ORP. I suspect this is caused by the organic gluconate rather than the ferrous component. Compounds that I would expect to raise the ORP figure (i.e. more positive) would be oxidizing agents such as hydrogen peroxide or potassium permanganate. In marine reef tanks, they also use ozone.

JPC

 

[jaypeecee]

That's why I asked what the ORP measurement was on a saturated fresh water sample, as that should be the theoretical maximum.

Hi @Wookii

It's important to remember that oxygen (as O2) will have lower oxidizing power than, for example, ozone (O3). The key point here is that ORP is a measure of oxidizing and reducing potential. It is not simply a measure of dissolved oxygen.

JPC

 

[jaypeecee]

In <"Marcel's article">...

Hi @dw1305

You beat me to it! Had i not been doing other things, I was planning to reference Marcel's excellent article. That article, along with the others on his site are some of the best scientific studies in the aquatics hobby - in my opinion.

JPC

 

[jaypeecee]

Hi Everyone,

Further to the link that @dw1305 provided in post #64 above, I'd like to draw attention to another excellent article that is included on Marcel's website. Here it is:

GetWidth

It addresses the issue of organics leakage from aquarium plants. If you don't want to read the whole article, just stick with the opening paragraph in which it states "Plants, therefore, in a sense, care for their own zoological garden".

JPC

 

[Wookii]

Hi @Wookii

It's important to remember that oxygen (as O2) will have lower oxidizing power than, for example, ozone (O3). The key point here is that ORP is a measure of oxidizing and reducing potential. It is not simply a measure of dissolved oxygen.

JPC

Agreed John, but I’m trying to steer towards tools the aquarist might be able to use to influence ORP in terms of tank management. For example, we’re not going to start injecting ozone, but we might increase surface agitation to add O2, or increase water change to remove organics?

 

[jaypeecee]

Agreed John, but I’m trying to steer towards tools the aquarist might be able to use to influence ORP in terms of tank management. For example, we’re not going to start injecting ozone, but we might increase surface agitation to add O2, or increase water change to remove organics?

Hi @Wookii

OK, I see where you're coming from. I'll give it some thought and hope to get back to you later today.

JPC

 

[jaypeecee]

Hi @Wookii

OK, I see where you're coming from. I'll give it some thought and hope to get back to you later today.

JPC

Hi @Wookii

It ought to be possible to increase ORP (i.e. more positive) by use of suitable filtration. I'm referring to the likes of Purigen or other organics removal media. Granulated activated carbon or other adsorption materials should be effective. If my memory serves me well (!), I seem to recall that you used to be a Purigen user.

JPC

 

[John q]

Lovely discussion, however is orp of any importance in a planted tank, I suspect not, 🤔

 

[dw1305]

Hi all,

Lovely discussion, however is orp of any importance in a planted tank, I suspect not, 🤔

I' m sure you are right, it is back to plants being <"the gift that keeps giving">.

Cheers Darrel

 

[jaypeecee]

Lovely discussion, however is orp of any importance in a planted tank, I suspect not, 🤔

Hi @John q

Would you care to explain, please?

As an example, aquatic plants release organics into the water and this will have the effect of lowering ORP. Organics are then mineralized by heterotrophic bacteria, consuming dissolved oxygen in the process. It's not the ORP figure in and of itself that's important. Instead the ORP figure is a proxy indicating what's happening in the water. It may not pinpoint the exact cause of the varying ORP figure and further investigation will probably be necessary. It's a bit like using a conductivity meter, which can only indicate changes in electrical conductivity. But, it will not indicate which ions are present in a water sample.

JPC

 

[John q]

It's not the ORP figure in and of itself that's important. Instead the ORP figure is a proxy indicating what's happening in the water.

Fair enough John, if we monitor the trend of orp then that could well give us an indication that's somethings amiss.
I just worry chasing a specific number, and potentially having someone adding chemicals to maintain that number isn't of any use in a planted tank.
To me if we have healthy plant growth and healthy fish, do regular water changes, and keep up with tank maintenance, the orp figure itself isn't of any particular value.

Sorry to derail the thread @MichaelJ

 

[dw1305]

Hi all,

if we monitor the trend of orp then that could well give us an indication that's somethings amiss.

Yes that is true, but I agree with @22802 & @MichaelJ things would need to be very, very amiss before the ORP meter gave you an indication.

If you kept <"big messy fish, at insane stocking rates">, in a non-planted tank and attempted <"simultaneous nitrification and denitrification in your filter">? Then an ORP meter would give you an indication of imminent (and inevitable) disaster.

cheers Darrel

 

[MichaelJ]

Lovely discussion, however is orp of any importance in a planted tank, I suspect not, 🤔

Well, that's what I am trying to figure out by having this discussion.

To me if we have healthy plant growth and healthy fish, do regular water changes, and keep up with tank maintenance, the orp figure itself isn't of any particular value.

That's where I seems to be at as well at this point as I've mentioned above:

the many times I have tested, it comes out around 300 mV. (mostly a bit lower). It suggests this particular tank [may] have a rather weak ability to break down waste etc. While that may be so, the tank (plants and livestock) seems to be doing very well regardless, so I just don't see a meaningful correlation between what the measurement tells me and what I observe in the tank

Sorry to derail the thread @MichaelJ

Your not derailing anything mate. This is a very helpful conversation I believe.

While I will keep measure it for a while (pre-mid-post WC as mentioned above) to see if I can pick up some sort of trend I mostly consider it a curiosity at this juncture and not something that would make me change anything in the way I run my tanks.

Cheers,
Michael

 

[MichaelJ]

Hi @jaypeecee ,

I find that addition of Seachem Iron (ferrous gluconate) lowers the ORP. I suspect this is caused by the organic gluconate rather than the ferrous component. Compounds that I would expect to raise the ORP figure (i.e. more positive) would be oxidizing agents such as hydrogen peroxide or potassium permanganate. In marine reef tanks, they also use ozone.

As I wrote above in my Journal entry #25 I've been experimenting with Ca/Mg Gluconate for remineralization in the past. Unfortunately I didn't own an ORP meter back then, but I think I probably would have measured a big mV drop if I did:

I have tried with Ca Gluconate and Mg Gluconate. Gluconate is an organic compound made from aerobic fermentation of sugar. Especially the high dose of Ca Gluconate needed to reach 27 ppm of Ca appears to cause a very undesired clouding of the water - possibly due to bacterial bloom or some unknown (to me) chemical reaction. I have tried to find a ratio between CaSO4 and Ca Gluconate where it didn’t cause problems, but the ratio ended up being so high (6 CaSO4 : 1 Ca Gluconate) that it wasn’t worth the extra effort. I have noticed some fertilizer products use Gluconate such as Seachem Iron, but with the tiny amounts needed to reach 0.5-1.0 ppm of Iron, the Gluconate will probably not cause any issues at all and Fe Gluconate is supposedly superior to chelated Fe - yet, I have actually seen some postings on other forums from people complaining about cloudy water after using Seachem Iron - anecdotal, for sure.

Cheers,
Michael

 

[MichaelJ]

WC Day

I was out of town for 10-11 days and didn’t get the chance to follow through on my 11-12 day WC plan… so this time around it's been 15 days.

Pre-WC measurements:

TDS 107 ppm - a 4 ppm increase. The increase is a couple of ppm’s lower than what I usually expect for 12 days and this was 15 days… In part, I guess its due to the less frequent feeding while we were traveling (manual feeding every 3 days and granule every day using the Eheim feeder) , and only doing one dosing of micros in 15 days and perhaps having a bit less evaporation than usual.

ORP 291 mV a 6 mV increase. I am not sure what to make of that - I thought 15 days of "waste buildup" would make it decrease 🙂 - not necessarily a lot, but at least some I would guess. It's possible that when I measured the last time after WC I just didn’t have the probe sitting in the tank long enough - I don’t think thats the case, but its possible.

What else.... well, removed a couple of dying/struggling leaves and some overgrown ones. As said, my submerged plants are in excellent health; slow growth, shred a leave here and there to give room for new growth - and relying on me to get rid of struggling leaves, or leaves that have outgrown the tank. Cleaned internal filter sponges (on the Pat Mini's), Replaced ~35% water.

Of course, a lot of Duckweed and Frogbit weeding, as usual 🙂 ... Yes, its getting long in the tooth.


All in all, with the water already prepared the day before, it took me about half an hour this time to do the maintenance on this tank. (not counting waiting for the ORP measurements which I will only do occationally).

The lower PO4 dosing mentioned in post #48 is not showing any effect - neither positive or negative. I didn’t expect (or wanted) anything different in just a couple of weeks anyway - it will take a while before the tank balances out around the new PO4/P dosing level.

Post-WC measurements (after 20 hours and trace dosing):

TDS 100 ppm. WC water was around 91 ppm so the tank TDS post-WC is where its supposed to be. More often than not, it’s a few ppm’s above actually.

ORP 311 mV. A 20 mV increase in ORP after WC. That seems reasonable.


Cheers,
Michael