Surprising O2 saturation levels

Mortie31 · Jun 23, 2018

Hi All
I’ve just installed a GHL oxygen sensor to my 750L reef tank, and I’m a little surprised at my O2 saturation levels , they have so far varied from 98% during the day and dropped down to a low of 88.4% now at 9:40 in the morning. It will be interesting to track these over the next few days. I assumed that I have sufficient flow, skimming and surface agitation that I would have complete saturation at least if not super saturated O2 levels. I have an MP60 and MP40 on 100% reefcrest, a gyre 230 on 100% variable flow. 4800L/hr from my return pumps and I run an RE double cone 200 skimmer 24/7. These levels don’t appear to be causing any issues for my tank, but there just not what I expected, I have calibrated the probe several times and am confident in that. My Ph varies from 8.09 to 8.36 over 24 hours, temp is 26.4C, KH is 7.5, Ca 450. Nitrate 15 - 20 and PO4 0.04. What are people’s thoughts as I seem to have a pretty typical reef with maybe higher than average flow yet I’m not hitting supersaturation. So a few things to ponder, are these results typical? Do O2 levels need increasing? Do these readings have any relevance at all? Are we assuming we have enough O2 in our tanks?
Cheers Paul

Randy Holmes-Farley · Jun 23, 2018

Most reefers just assume they have complete aeration by looking at the water movement, when a simple measurement of the diurnal change in pH usually proves otherwise.

That said, I do not know if your measurements are accurate, or for that matter, what O2 levels are Ok and what ones are not. See Figure 19 in the last article below for O2 on actual reefs, which also is not always saturated.

Eric shows a lot of O3 measurements and discussion here. It is possible that his device was reading saturation lower than it really was since some of his results are most readily explained by a systemic error reading a bit low (e.g., a rise in O2 from below 100% when turning off a powerhead in Figure 14)

The need to breathe in reef tanks: is it a given right? Reefkeeping 4(5) http://www.reefkeeping.com/issues/2005-06/eb/index.php

The need to breathe, part 2: experimental tanks. Reefkeeping 4(6) http://www.reefkeeping.com/issues/2005-07/eb/index.php

The Need to Breathe, Part 3: Real Tanks and Real Importance
http://reefkeeping.com/issues/2005-08/eb/index.php

Cory · Jun 23, 2018

Im thinking an oxydator would help and or an ats. Surprising to me too!

MnFish1 · Jun 23, 2018

Mortie31 said:
Hi All
I’ve just installed a GHL oxygen sensor to my 750L reef tank, and I’m a little surprised at my O2 saturation levels , they have so far varied from 98% during the day and dropped down to a low of 88.4% now at 9:40 in the morning. It will be interesting to track these over the next few days. I assumed that I have sufficient flow, skimming and surface agitation that I would have complete saturation at least if not super saturated O2 levels. I have an MP60 and MP40 on 100% reefcrest, a gyre 230 on 100% variable flow. 4800L/hr from my return pumps and I run an RE double cone 200 skimmer 24/7. These levels don’t appear to be causing any issues for my tank, but there just not what I expected, I have calibrated the probe several times and am confident in that. My Ph varies from 8.09 to 8.36 over 24 hours, temp is 26.4C, KH is 7.5, Ca 450. Nitrate 15 - 20 and PO4 0.04. What are people’s thoughts as I seem to have a pretty typical reef with maybe higher than average flow yet I’m not hitting supersaturation. So a few things to ponder, are these results typical? Do O2 levels need increasing? Do these readings have any relevance at all? Are we assuming we have enough O2 in our tanks?
Cheers Paul

According to Randy's article - supersaturation doesn't happen without photosynthetic activity (which is why its lower in the AM after the lights were off). Also that water flow from pumps doesn't do much to influence oxygenation - but that skimmers and hairstones do. What is in your tank?

MnFish1 · Jun 23, 2018

BTW can't you check the DO as well as the saturation with that meter? I.e. in mg/l?

Mortie31 · Jun 23, 2018

Thanks for your replies all... I’ll read the articles later Randy, thank you. I performed several calibrations of the O2 probe and the salinity probe, which along with the temp probe is used to calculate the O2 saturation. Other than that I don’t know how accurate these probes are.

Mortie31 · Jun 23, 2018

MnFish1 said:
According to Randy's article - supersaturation doesn't happen without photosynthetic activity (which is why its lower in the AM after the lights were off). Also that water flow from pumps doesn't do much to influence oxygenation - but that skimmers and hairstones do. What is in your tank?

I have a large skimmer and 3 powerheads, but no air stones in the system, wouldn’t water flow from a return pump directed at the surface would have an impact on levels?

Mortie31 · Jun 23, 2018

MnFish1 said:
BTW can't you check the DO as well as the saturation with that meter? I.e. in mg/l?

The DO is 6.53, which is slightly lower than the levels in table 1 in part 1 of the articles linked by Randy, but isn’t far off. I’m actually reading 98.9% (5pm) saturation now as well, levels have slowly increased since my lights started to ramp up.

Mortie31 · Jun 23, 2018

Cory said:
Im thinking an oxydator would help and or an ats. Surprising to me too!

Is putting Hydrogen peroxide into a tank safe? Just looked at the oxydator and they look interesting and I know #Lasse swears by them

Cory · Jun 23, 2018

Mortie31 said:
Is putting Hydrogen peroxide into a tank safe? Just looked at the oxydator and they look interesting and I know #Lasse swears by them

Yes in an oxydator it is. It doesnt put peroxide in the water. If any gets through its very minimal.

jasonrusso · Jun 24, 2018

Mortie31 said:
I have a large skimmer and 3 powerheads, but no air stones in the system, wouldn’t water flow from a return pump directed at the surface would have an impact on levels?

Agitation causes gas exchange. So a powerhead at the surface or a skimmer works. The bubbles coming from the airstone aren't dissolving in water, they are causing turbulence at the surface.

Randy Holmes-Farley · Jun 24, 2018

jasonrusso said:
Agitation causes gas exchange. So a powerhead at the surface or a skimmer works. The bubbles coming from the airstone aren't dissolving in water, they are causing turbulence at the surface.

But the air inside the bubbles is also aerating the water. :)

Mortie31 · Aug 11, 2018

I’ve had the Oxygen probe for several weeks now and it’s been interesting to see how powerhead placement and overflow water height affect the levels, dropping the water level in my overflow by several inches really increased the O2 levels significantly but the noise drove me mad. Surface agitation seems to be the determining factor in my tank, I run 2 vortech power heads and these don’t seem to contribute a huge amount to my O2 levels if I run them 2/3rds of the way up in my tank as I like to. If I rise them in my tank O2 levels rise, I’ve found the best way for me to strike a happy balance is to have my Gyre pointing at the surface, I can keep my vortechs lower in the tank and my overflow silent, I have an Oxydator in the tank now which raised O2 levels by about 5%. Levels drop significantly overnight. I guess nothing surprising in the results but I wouldn’t like to be just running Vortechs alone in my tank at the depth I have them at now, but saying that is 102% sat O2 not high enough?

Randy Holmes-Farley · Aug 11, 2018

Interesting. I'd like to play with O2 that way. :)

I don't think we really know if 90% O2 saturation vs 100% saturation will led to any apparent difference in a reef tank.

Mortie31 · Aug 11, 2018

Randy Holmes-Farley said:
Interesting. I'd like to play with O2 that way. :)

I don't think we really know if 90% O2 saturation vs 100% saturation will led to any apparent difference in a reef tank.

Unfortunately playing is all I’m doing, it’s interesting, but as there are too many variables nothing can be ascertained, but I will think more in terms of surface agitation and powerhead placement, I may well measure how quickly O2 depletes during a powercut next and if battery backups do help or not.

MnFish1 · Aug 11, 2018

Mortie31 said:
Unfortunately playing is all I’m doing, it’s interesting, but as there are too many variables nothing can be ascertained, but I will think more in terms of surface agitation and powerhead placement, I may well measure how quickly O2 depletes during a powercut next and if battery backups do help or not.

Where is the probe kept in relation to the flow?

Mortie31 · Aug 11, 2018

MnFish1 said:
Where is the probe kept in relation to the flow?

It’s in the sump, I placed it there to give a consistant reading of overall system O2 levels

2una · Aug 12, 2018

i sit at around 90% - thought that was surprising as i run 2 skimmers, initially put it on to see if maybe i was oversaturating as i've always battled getting denitrification happening without using some forced way.(denitrator)

Mortie31 · Aug 12, 2018

2una said:
i sit at around 90% - thought that was surprising as i run 2 skimmers, initially put it on to see if maybe i was oversaturating as i've always battled getting denitrification happening without using some forced way.(denitrator)

Is your 90% the minimum level you are getting what’s your peak value?