Lets talk about dissolved O2

Indoor Growing Hydroponics
#1

I am curious about dissolved O2. I suspect I am over aerating (see diagram below) but I want to error on the side of too much aeration to ensure max saturation.

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I have seen the temp/salinity charts that show the maximum possible.

This is my sump, a future endeavor will be to incorporate a waterfall type backsplash for the return to pour over.

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One question is what is the minimum O2 level to support aggressive growth?

I feel like I have more than enough aeration, but I would like to measure the dissolved O2 to validate how much aeration is actually needed. Maybe I can eliminate one of the air pumps.

What have you folks found to be the best way to measure the O2? I see some meters, and titration type test kits for the aquarium hobby. What is the best bang for the buck?

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#2

I don’t measure dissolved 02 but I keep a ln air pump running 24/7. Allow the return to drop and splash back in the Res. And add h202 once a week which dissolves into oxygen and water. It’s more than sufficient bro

Edited to say I run F&D not RDWC

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#3

I wouldn’t go under 5ppm of 02, that’s about what tap water has.
7-10 ppm is the recommended level. Levels of 12-15 is considered excessive.

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At 1 atmosphere 1ppm = 1mg/l

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#4

When I first started growing with DWC I had big 35w air pump going to 4 buckets. While the plants were small everything was fine. As they grew I found 2 males that I pulled and decided to plant a female outside. So at that point I had that 35w pump devoted to one bucket. Wasn’t long before I was seeing frequent major down swings in pH. I couldn’t figure it. I read that some types of biology could bring pH down so I took steps to mitigate that. My roots were white and my water was clean. Still didn’t stop. I was adding pH up every evening and morning. Was lucky enough to come across a post on ICmag I think it was. It was talking about Acid Rain Effect in reservoirs in DWC. From what I recall, as you pump air in there to get dissolved O, youre also pumping CO2 in there and it can add up making the rez acidic. I adjusted the valve on my pump and that fixed my issue. This is purely anecdotal, after my issue was fixed I didn’t look any further into the matter but it might be something worth knowing.

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#5

I understand salinity in the context of aquariums, I raised African Chiclids for 30 years.

" Salinity is the dissolved salt content of a body of water. It is a strong contributor to conductivity"

The nutrients are salts. How does 800ppm of nutes affect the salinity?

So if I am understand the charts above, I have to consider that nute solutions, increase salinity.

Any charts that show dissolved O2 in salinities of 800ppm?

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#6

Here you go, @MrWizard

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#7

Awesome!

So to make sure I got this right:

at 25C, and 1000 ppm, I would get 7.807 ppm maximum saturation.

Is this accurate?

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#8

The second graph I posted mentions salinity ~35. That’s calculated in parts per thousand… 35000ppm :sweat_smile:

Even with this amount of salt, the solubility of 02 varied by around 1 point. 800 ppm effect on 02 is negligible.

Temps play a more important role…

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#9

I get 8.22 using this calculator.

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From
https://www.colby.edu/chemistry/CH331/O2%20Solubility.html

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#10

Awesome sauce, THANK YOU!

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#11

So now I know how to calculate the physical maximum saturation. Thanks for that.

What is the most practical way to measure dissolved O2?

I want to measure the O2, assuming I am at saturation I want to reduce aeration until I see the O2 drop.

As mentioned, a lot of aeration does affect the pH. Would love to minimize that affect.

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#12

image

So, I can look at my Guardian and calculate that the maximum saturation would be 8.03

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Now I need to measure the actual.

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#13

I double checked to be sure, the calculator is accurate :+1:

After running rdwc for 10+ years with pumps, I strictly roll with a waterfall and it’s perfect.

I never measured the 02, I think heath did. He bought a few gadgets… the $$ one were good. :sweat_smile:

Edit
The solubility calculations give you the saturation point. What’s in the water is a mystery.
If there’s tiny bubbles on the sides of your container, you’ve hit saturation.

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#14

You’d really need a D.O. meter to know how much you have… Cheapest are around $100 and they only go up from there…

I do flood and drain, and with 2 to 4 hour intervals between floods, I found I do not need to run any airstone or otherwise to aerate that water. Just the act of flooding the tray for 1 minute every few hours is more than enough for the plants.

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#15

Is something like this a waste of money? Is it accurate enough?

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#16

You could run something like this for a cheap, lab-grade option but it needs an Arduino or something to power it:

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#17

I mean… I would think all of them are kind of a waste of money. Assuming it works you’ll need it all of 5 minutes and then never touch it again :sweat_smile:

What kind of system are you running again? RDWC? if it’s RDWC I’d use waterfalls in the buckets and you don’t need anything else. The constant churning of the waterfall will fully saturate it all.

You should be able to deduce oxygen levels from checking/smelling the water and looking at the plants. Stale/Old water usually gets a film on the top and doesn’t smell good nor “fresh”.

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#18

Yes this, CO2 will combine with water to male carbonic acid. I think this would be the issue you would see long before an issue with too much dissolved oxygen.

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#19

To be clear.

My objective is to see if I can reduce the # of air stones and eliminate a pump if I can. Eliminating a pump will save energy, expense, and complexity. I.e. simplify the setup. However, I need to prove to myself that I am reaching saturation in the process.

I really do have a gut feeling that I am currently way into overkill territory.

Is there a way to calculate how many liters per minute of supplemental air are required for a volume of 20 gallons at a flow rate of 500gph?

#20

If your setup is the one pictured above, I’d say it’s overkill for a 20 gal setup. Hell just one 50w air pump is overkill IMO. And air stones? Chuck 'em. They need replacing every few runs and could cause contamination problems if not cleaned properly. @JoeCrowe showed me his use of a stainless nut with a ‘T’ and I’ve been rocking that ever since.

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