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[APD] CO2 revelations

CO2 is one of those critical things that aquatic plants folks should really focus on.
I've nagged folks about this for a very long time, and I will likely nag you to the grave.
Complacent experts, newbies, test kit freaks, all of you(and myself included).
Poor CO2 reduces growth and is responsible for nearly 95% of all algae related issues. 
Now KH test kit variance is one issue, making a reference standard to compare you KH test to is a very WISE idea to check the accuracy. I've seen many folks have very high CO2 predicted levels, yet fish were fine, but another than has barely 30ppm and the fish are gasping. It cannot be that both are at the same CO2ppm level becaused we would expect to see the same behavior from the fish. Instead we see very wide ranges and impacts on the fish(as well as plants).
So it's much more likely that it is the testing method, rather than anything else.
pH is the best thing as far as accuracy for CO2 measurements using a pH probe and no electrical equipment runnign when the pH is measured(stray current will depress the pH giving false high ppm CO2 levels).
KH test kits have consistency issues (see recent post) and in some places, although rare, non bicarbonate alkalinity exists(recent poster in NM has significant borate alkalinity, desert regions generally).
Addressing this issue by making a reference sample will take care of the KH issue.
The next issue is more interesting for many of of you.
I'd suggested that the venturi DIY reactor I have shown folks on my site is better than any reactor. Well, initially, and perhaps partially true, is the purpging effect of gas build up.
This gas is some O2 and some CO2, but very little "air". 
As the gas is expelled, consistently I see better growth, this is not due to O2. 
So why would a mist of tiny CO2 bubbles vs dissolved CO2 in solution do better for growing plants?
I addressed the O2 issue simply, I used a diffuser disk for CO2(no O2 gas build up occurs).
But that did not do it __alone__.
I wondered why.
So I placed the diffuser disc near similar current like that produced by the venturi reactor after is starts mistuing the gas out the bottom.
Lo and behold, Bam! Excellent similar growth.
Not the kind of so so growth, but pearling like nothing you have ever seen or perhaps only in a  very few well run tanks right after a water change. But I'd not done a water change for a week.
I tried it several times on 4 tanks, same result in each tank. Day after day, intense pearling even with fair good current. 
So why would this mist be better than dissolved CO2?
For one thing, it's __pure CO2 gas__, which flows much faster than dissolved CO2 liquid.
The flux rate is much faster with pure CO2 gas than CO2 dissolved in water, so the plants get more CO2 and a more concentrated form.
Some folks may not like the bubbles, some might not like pearling.
But I sure do.
I can say that the venturi effect is one of CO2 now, and not of O2 by using the diffuser disc to rule out O2.
So that just left CO2 and the gas vs dissolved form to consider why one method was better in terms of plant than another.
Both flow and actually having some gas in the tank itself seems to be the key here. 
So those disc are not so bad and neither are the venturi reactors.
You can make a purge loop for external reactors by making a hole 1/2 down and running the air line back to the intake for the power head, caniter filter etc, this will not add bubbles but will reduce the gas build up inside the reactor.
The real issue is having gas bubbles in the tank and putting them where the plants are in that form.   
I think folks should really consider this/these idea/s and try them.
I've had very intense pearling and have over the entire routine time frame, not just for a day or a few days.
Be careful and watch the fish, CO2 levels when doing this, I've not had any fish issues yet. Make sure there is some surface movement. If you use disc, clean them often(monthly). 
For larger tanks, they make 6x1" diffuser stones for about 60$ than can be used set along the bottom back gravel layer so they will not be seen. wwww.aquaticeco.com sells them if interested. 
In any event, this notion of having tiny gas bubbles floating around very dissolved CO2 might solve many folk's problems and improve those who seek better growth.
Nitrogen is an essential element, but only 1.5%, vs 40+ % for Carbon, it is very very wise to focus on this if you seek better growth.
With good CO2 levels, even the wimpy plants do very well(Tonia, ES, Eirocauleon) algae dies, pearling as intense as you have ever seen it day after day will occur.
I think the gas bubbles might also be less of an issue for fish since it's not dissolved into solution also.
The nutrients can be addressed easily by doing EI, so you know there's enough, so all that's left to really focus on is the CO2.
So I have been playing around trying to figuire out a good way to reproduce max CO2 without causing issues for fish, and adding enough for the plants.
The CO2 mist + current seems to be the best method.
This can be done with a reactor or a diffuser stone/disc.
Also, folks using spray bars, turn them vertically, next to the intake and place the disc down near this also. This hides the bar, the disc, intake all in one place. Having the spray bar current blowing along the back side the tank wall seems to give good flow characteristics+ near the disc, the water blows out and away from the intake and circles around to the intake.
Since water is being blown directly away from the intake, this gives optimum mixing.
Since water is being blown directly on top of the difusser, all the bubble mist is being blown all over the tank.
The results are easy to see.
The other issue is not to trust the test kits so much until you see the type of pearling like this, no BBA growth etc, slowly and patiently add more CO2 till you get the pearling and good growth. Basically use the test to get close, then tweak(add more) carefully and slowly.
Do not go overboard, do it slowly and observe the plants/fish. Your test may give you high numbers, but if the fish are fine, then it's okay.
Turing off CO2 at night will help add the margin of safety also. We add CO2 for the plants, not to maintain pH. Some leave it 24/7, but mainly out of convenience rather than methodology. With disc, running them at night can cause issues, anyway, you can save 2-3x the gas by not running it at night. We know fish don't care about the pH change.
Tom Barr 

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