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Trickle Filters and CO2

There has been some discussion of aquariums with trickle filters requiring a
high input of CO2 in order to get an adequate level of CO2 dissolved in the
water.  I have a 100 gallon tank with a built-in overflow and a trickle
filter.  The CO2 is injected via an Eheim diffuser on the bottom of the
trickle filter.  It has been running for two years.  When I was setting up
the tank I ran experiments as to how much CO2 (bubbles per second) were
required to get about 15 mg/l.  Initially I found that even with the
overflow box and the trickle filter sealed with tape, I needed to dump
massive amounts of CO2 into the water to get the 15 mg/l.  When I reduced
rate of return flow into the tank the amount of CO2 need to be injected
dropped drasticly.  The spray tubes with holes pointed downward are mounted
below the water surface along each side of the tank (18 inches long each).
If the water flow is high enough to cause ripples in the surface the CO2
left the water at a very high rate.  If the flow rate was cut down so that
there was no movement on the surface of the water, then only 2 bubbles per
second were needed to achieve the 15mg/l.  After discovering this, I
searched the Archives.  Lo and Behold, there was discussion in the Archives
that indicated that surface agitation would drive off CO2 at a very high
rate.  My experiments merely confirmed what was already documented.  Guess I
should read the Archives first.

So, if you are injecting a lot of CO2 but not getting much dissolved in the
water, try reducing the surface agitation; i.e.make the surface glass
smooth.  Of course that reduces the filtration of the tank - always
trade-offs.  With the reduced water flow through the trickle filter the
water in my tank was not crystal clear.  So recently I have added an Ehiem
canister filter to the tank - again being very careful with the return flow
to keep the surface glass smooth.  The trickle filter keeps the heater and
diffuser out of the tank, which I like and the canister keeps the water
crystal clear.  Now, is there any way to combine the benefits of both
filtration systems into one filter?

As additional info, I refill my 10lb CO2 tank about twice a year at 2
bubbles per second.

Best Regards,

Roger Gordon