If you are in South FL USA, I'll do that trade in a second!

No, no gradient noted.
At least in the tanks I measured.
There was a gradient however from top[ to bottom, but it was due to current, no outgassing near as I can tell.

Also, the closer to plants,, high or low in the tank, the lower CO2 became.

So I'd say the distance from the surface seemed to have less to do with it as flow/current and plants/light.

Regards,
Tom Barr

Well said Vaughn.

Really well said.

I've long held this belief about CO2, but so many folks on firums and the web in general only give a passing glance to CO2, the study, and mechanics of how it gets to plants in real tanks, real plant beds etc.

Others merely tell folks 30ppm and that's it.
Or some have tried returning to 15 ppm etc with limiting nutrients etc, when if they had just added more flow, they'd not had failed at higher levels.

Regards,
Tom Barr

I think most hold Vaughn's attitude about a lot of what I say, until I can show them in person and then they can measure and prove it to themselves.

Trying to convince wind bags, blow hards(no one here, but a few other forums and news list over the years) about this is quite a challenge.



Regards,
Tom Barr

If you're enjoying the tank, you're not doing it right

Ok, seriously though. Very interesting stuff. Anyone have any thoughts on dealing with this issue beyond turning the tank into a whirlpool? Multiple injection sites for CO2? Primary CO2 injection site somewhere inside a plant bed?

Ah, another thing...any correlation between "dark spots" and areas of lower CO2? It might make sense to assume the areas with lower flow might also be getting less light which would make less CO2 pseudo appropriate.

I'm testing some things in the tank that it's now installed on, a 1600 gallon 12 ft long monster.

So there are a few "problem areas", well one, really.........
So I'm having the probe stuck over there for now.

See what it does, then move it around elsewhere.
We can answer quite a few CO2 questions.
Also, we have nutrient(colorimeter) and light(PAR) data as well.

Regards,
Tom Barr

Well put!

I wonder why no one has mentioned co2 injected into the plant bed, don’t most people do this with hydroponics? Is it the fact that it would be difficult to evenly disperse that causes us not to try it? Could we burry multiple air stones around the gravel bed and have sets of tubes pumping co2 into each? Since primary nutrient intake is via the roots i would assume the above true. What do you guys think?


What did the nutrient meters find out about nutrients around the tank? Do they also form a gradient?

Once you eliminate the outgassing of CO2 at the surface as a major contributor to the wide variation in concentration of CO2 in the water, you are stuck with assuming that all nutrients are equally variable in the water. That is because you are left with the plant's consumption of nutrients as a primary cause of the variations. CO2 is just a nutrient, like nitrogen, potassium, etc., if you can discount the effect of outgassing.

A few weeks ago I watched George Farmer's very well done video where he set up an aquascape that featured a pile of rocks near the center of the tank, planted with plants tucked into the crevices, and with the outer areas all relatively free of large plant masses. That got me to thinking that this is the basic aquascape of the future, because it leaves room for good water flow all around the tank. I have switched to this form from my usual tall in the back and sides, with lower in the middle aquascape. My usual aquascape would very soon become overgrown and that plant mass would stop the circulation, leaving me with BBA starting.

This is just one of the possible directions this hobby might take once we realize how important good water circulation is. Another is, as noted above, a different method for introducing CO2 at multiple points in the tank. But, that leaves the other nutrients needing better distribution.

I thought the comments on the George Farmer tank were interesting. I have had some problems getting good circulation in tanks without creating a tsunami. Watching my vals lie parallel to the substrate is not very attractive. Maybe we do need to start paying more attention to how tanks are scaped. If one has large masses of plants the entire length of the tank it may be that no amount of circulation will be enough.

Tom's measurements were striking. It appears that we need 30 ppm of co2 not because the plants need that much co2, but to compensate for the fall off. If we could really improve circulation perhaps we would not need 30 ppm. Maintaning that level can be difficult even with pressurized equipment.

A. No, this is not the primary route for plants, they can and do take it in from both locations, always have. Even if you are a terrestrial plant, you still retain the ability to take up foliar applications, if I have no nutrients in the sediment, and flow is resistricted due to fine grain sand, then obviously the plant must get it from the water column.

Plants are opportunistic, roots, or shoots.
90% of all terrestrial ornamental plants are fertigated, the soil they grow them in is sand and bark, no nutrients. They pack them in a mix and ship them in soil in most cases, but they do not grow them this way.

There might be some nutrient gradients in soils, but not water column unless flow is low and the levels of nutrients are low. CO2: it's far far more volatile/transient.

Regards,
Tom Barr