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.


Regards,
Tom Barr

www.BarrReport.com

Yikes, I just made this. http://www.hoftiezer.net/personal/aquaria/ Some glue is curing as I wright this. I wanted to get this http://www.aquariumplants.com/cgi-bin/cart/pr009.html outta the tank. Maybe I will rethink this a bit.

Rick

Hi Tom,

On another board, you helped me with a non-CO2 30Long, High Light system and you were right. I floundered and last Friday, hooked up an old Aqua Medic CO2 reg, bubble counter, new PH Monitor and full tank but I didn't have a diffusser. I looked around and had an old Duetto DJ-50 inside filter that has an aerator built in on the top of the filter. I installed the CO2 hose into this, new sponges and instant CO2 diffuser that is putting out a fine mist of CO2 bubbles which then get caught in the current from my Power Head on the UG (not a RFUG unfortunately). My CO2 is at 30ppm and plants are growing like crazy. I can't tell, though, if the plants are perling or if the fine mist of bubbles is just collecting on them and then rising. Seems to work well though.

Thanks for the Help

Mike

very good point here...how do you know??

I have been looking at the venturi you have on your DIY page. I think I can use the external reactor I made, to put on the output of my canister, in the same fashion.

I will drill the two small holes 2" and 2.5" down on the external reactor tube. I will route the hose from the one 2" down into the venturi input to a power head in the tank and route the hose from the the one 2.5" down to spill anywhere into the tank.

I think the top outlet might give the in tank power head a similar mist of CO2 bubbles and the bottom outlet will burb or expel any excess gas.


Rick

Tom, could it be that those bubbles "flying" out of the DIY venturi reactor are actually O2 bubbles being caught onto plant leaves and not from plant growth?

Regards
Peter Gwee

Tom,

There is an interesting experiment you could try along these lines. I used to work for a company that has a membrane based gas/liquid exchange technology. Been awhile since I worked for them - but using thier modules - should be able to get max CO2 concentrations into the water. There would be no mist or bubbles - its an extremely efficient diffusion reactor. I have been trying for awhile to get them to send me one (they probably won't because I am sure they think I am working for some competitor and the aquarium story is a ruse). This is the stuff used in heart lung machines for blood oxygenation/co2 removal.

Only down sides are biofilm forming on membrane and impact on efficiency and cost. You would have to clean them after awhile possibly. Any interest? I can pursue it a little more. You would be the right guy to test since you have the "other data" as reference point and observation.

Terry

Well, hehe, enter the diffuser disc, which has no such issue as a control for this same issue.

Same observation............

Try again

Sorry Terry, biofilms and passive reactors are not my thing.
Bioflim issue is a biggy.
Our lungs diffuse CO2 out/O2 in through liquid(our blood) the same way as reactors do. Gas is much easier to breath in and we get far more exchange than we would with water(this can be done with super sat O2 liquid and deep sea divers etc, but you can breath much better with O2 gas!)

Mike, see the control I used with the disc, so the answer is no, it's plant production.

You can also do a O2 test and see if you have higher O2 levels with or without(this is what I did as well as simply observe plant health etc).

I think this will bug folks for a long time.
It's counter to what you woud think, since saving every last bubble seems "better" and would produce better growth, but it is an issue of delivery and in what concentration(100% CO2 gas).



Regards,
Tom Barr

Tom, how about feeding the CO2 gas into a powerhead output with a spraybar at the bottom back area of the tank? Loads of misting around in the tank and the bubbles gets to all parts of the plants pretty good. Frankly, I did get that result some time back when you suggest that method of a powerhead with spraybar but thought those were some form of gases and not real pearling.

Regards
Peter Gwee

tom,the issue of a staginate 55 gal tank i asked about in recent thread has responded to turning co2 way up to increase small bubbles coming out of bottom of diy reactor. also set sraybar to get surface motion. this tank has never pearled. now there is action everywhere in tank. could this be the step in the right direction? i am finding out that co2 and more co2 is the only way for a successful tank. thank you, regards,cornhusker