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DIY CO2 bubble size

troi said

The instructions on the KRIB say I should use about or two bubbles per
minute. I am using a glass bead, low back pressure air stone on the air
line, but cannot get "one or two bubbles per minute." Without an in-line
air valve, I get a nearly steady stream of small, not tiny bubbles.
With various adjustments, I got bursts of bigger bubbles every 2 or
three seconds, streams of tiny bubbles, or very slow, but steady,
streams of small(vs tiny) bubbles. The instructions don't say what size
bubble should escape once or twice a minute, or if a burst of bubbles
from an air stone counts as one whole bubble or several bubbles.  Iam
confused and concerned.

Wayne replies

You can adjust the outout of a sugar/yeast generator by changing the recipe
you use and by using different bottle sizes or using more than one bottle.
There are a lot of variables involved and I do not think there is any way to
get an exact measured amount of CO2 out of this kind of system. Basically
though, increasing the amount of yeast will increase CO2 production and
using a larger bottle will also increase production. Adding yeast nutrient
at some time during the fermentation will also dramatically increase
production and using more than one bottle started at different times will
also tend to even out CO2 production. You should not try and adjust the flow
of CO2 by choking off the supply this can cause your bottle to burst.

I use 2 one gallon jugs that are started one month apart in both my 90 and
120 gallon tanks. Smaller tanks should use smaller bottles. The recipe I now
use is 1 tsp. of wine yeast, 2 tsp. baking soda and 4 cups of sugar. I add
enough 105 degree water to the jug so that the S.G. is over 1.086. After 15
days the production starts to drop off and I then add 1/2 a tsp. of yeast
nutrient. After 40 days the production again starts to drop off and then I
add 1/2 tsp. of "yeast energizer". After 6-8 weeks it is time to start over.

Counting bubbles with yeast sugar generators has always been a bit of a
problem for me a bit of a problem for me. I have never been able to make
anything that will truly and accurately measure CO2 production. If there is
a large airspace left in the generator bottle then the gas in the bottle
will compress a little until a bubble is released and then several will come
out at once. I now use a small pop bottle with a rubber stopper in it for a
bubble counter. More than one generator can be hooked to the same counter
and I can count the bubbles from each generator separately. If there is not
too large space for the CO2 gas left in the generator bottle usually the
bubble counter works pretty well. I find the ideal bubble rate for my tanks
is just about 1  bubble per second but this is going to vary a lot depending
on your particular setup.

In the end though it doesn't really matter how many bubbles are being
produced. What really matters is how the CO2 production affects your pH.
Since there is no way to completely control CO2 production with a
yeast/sugar setup, the easiest thing is just to measure the pH of your tank.
Measure the pH of your tank before you inject CO2 and monitor it after you
inject CO2. I shoot for a pH drop of between .4 and .8 below the normal tank
value. I get really good plant growth at .6 below normal. I would be
concerned if the pH fell more than 1.0 below normal. I think that trying to
control the pH more closely than this is unrealistic given the variation in
CO2 production

troi said

The Krib article also mentions upping the efficiency and diffusion by
sticking the line in an intake or a diffuser.  I am using a Rio 200
powered with prefilter and a small Aquaclear.  CAn I just stick the
airline in the box of the Aquaclear or run it into the Venturi input on
the Rio?  Of am I ok on a forty gal. currently lightly planted tank with
just the clumsy air stone? Should I go to a higher backpressure?

Wayne replies

There are a lot of ways to difuse the CO2 into your tank. For a small tank I
would use a bell jar type system which is not very efficient but self
limiting to certain degree as to how much CO2 gets disolved. For larger
tanks you need something more efficient. The simplest is to attach the end
of your CO2 line to the outside of your aquaclear intake with a rubber band.
This is suprisingly efficient but you have to regularily remove any debris
that accumulates around the intake or it will deflect bubbles away from the
intake. You must also keep your tank very full or the splashing of the water
will drive off the CO2 at the water surface. Another really efficient method
is to use a reverse flow difuser made from a power head and a gravel
cleaning tube. It is a little unsightly but works like a charm. There are
diagrams of this in the Krib and I like this method a lot. One thing that
really helps is to put a T in the output line from the power head before the
gravel tube. This will reduce the flow through the gravel tube and also
prevent CO2 from pushing water out of the pump impeller chamber in the event
of a power failure. If this occurs the pump may fail to prime when the power
comes back on and wreck your impellor. Another added advantage of addding
the T is excess gasses always build up in the gravel tube and to clear them
out you just have to shut the power off to the pump for a couple of seconds.

Recently I have started using another variation on this type of difuser. I
am using a medium size pump that sticks on the middle of the back of the
tank and has an aquaclear 500 sponge stuck over the intake. The output of
the pump feeds into a small T which puts some of the pump output directly
back into the tank. After the T I inject the CO2 and the balance of the
water flow goes into a 3/4" PVC spray bar mounted on the back of the hood.
The pipe is filled with some bits of plastic tubing that help to smash up
the CO2 before it gets put into the tank. I like this solution because it
looks good and I can completly control the surface agitation in the tank
while directing the water wherever I like. The system also distributes the
CO2 evenly throughout the tank, doesn't cost much, allows me to use a sponge
over the pump intake and cannot collapse my CO2 bottles. So far it has been
very reliable.