Nutrients, including CO2, are in the water to be consumed by the plants. As the plants consume them, they are no longer in the water. Areas of the tank where plants are consuming the nutrients rapidly will be starved for nutrients unless something moves more nutrients into that area to replenish those which were consumed. That is the role of water circulation. Diffusion of nutrients from high concentration areas to lower concentration areas isn't nearly as rapid as good water circulation is, and it depends on the gradient in concentration to make it occur, but we don't want gradients in nutrient concentration.

Neither you nor I have a good enough excuse to be lazy! That sucks.

very intesersting!
What would be the price of this product? probably quie expensive. but maybe a your local fish club can invest in such a device. I would be interested!

greets,

yme

Hoppy,

LOL.. Well, I was just hoping for that tiny bit of excuse.
Jokes aside, thanks for your explanation.

I always thought that the diffusion happens very fast (think about a drop of colored water in a pail of clear water)

So just a bit of circulation might boost that diffusion rate two-fold? ten-fold?

If we go low light, the uptake of nutrients is slower, will diffusion be enough to 'spread' the nutrients around?

I'm having this idea in my head about achieving 1mph in our tanks.
A wave-maker perhaps?

Regards,
Ryan

Calculating how fast diffusion happens is beyond the scope of this course. (One of my old college professors loved that comment!) Seriously, I have no good idea about how fast diffusion takes place, but I do know that when I add trace mix to my tank, the "cloud" of haze it causes doesn't disappear very fast.

Intuitively, you would have to conclude that low light tanks don't have nearly the problem with local nutrient depletion that high light tanks do. But, they also don't get the high nutrient concentrations that high light tanks get, so it could be that they need the circulation too. Tom's references on water circulation mentioned one mph as a water velocity that is good, but that is a very high current for a small tank. It is about 18 inches per second - about 2 seconds for all of the water on the left side to move to the right side! Since the flow in our tanks is very chaotic, it may be that eddies and other local water movement can be that high a velocity. In any case, it does give a feel for what good water movement really is.

Koralia type power heads, which use a "boat propeller" to move water, are very good for achieving the circulation we need - much better than ordinary power heads.

On my 300 gallon tank the current c02 distribution method is a diy reactor with a magdrive 9.5 and spray bars along the top pointing straight down into the plant bed. This is in addition to 2 xp3's an xp4 and various powerheads for a total of about 2500 gph distributed around the tank.

I have a plan to change it all over to a sump design with high flow, maybe wave makers etc. but after reading this thread I was wondering if the solution, in my case, is to put the spray bar down on the garvel pointing up. Is'nt it right down in the plant bed that Tom is measuring the least amount of c02? With the spray bar on top, I can't be getting any c02 at all down in the plant bed in my 30"deep tank.

Very easy to try before ripping all the plumbing out.

Steve

It does seem that the water containing the incoming CO2 should start its journey around the tank at the bottom of the tank. Any bubbles of CO2 would then have the maximum of time to reach the most plants before finally rising to the top of the water. Right now my CO2 is by a mist method and the Koralia which blows it around is near the bottom of the tank.