RE: [APD] Can one just give up?

[Bill Wichers <billw at waveform_net>]

> You could use a solenoid to open when the pH get down to a
> specific level. Have the Solenoid teed off the CO2 line
> that goes into the tank. When the solenoid opens, the CO2
> bleeds out through the solenoid instead of going into the
> tank. You won't be using any less CO2, but if, without the
> solenoid, it's dumping more than is desired, you won't be
> wasting any *more* -- and you won't be hurting the fish.

Actually, an SPDT solenoid (one common port and two others, energizing the 
solenoid switches gas flow from one port to the other rather than a 
strictly on-off action) would be perfect for this. Something like having 
the energized-active port sending CO2 into the tank and de-energized-active 
port sending CO2 venting to the air. This type of solenoid shows up at 
mail-order surplus places frequently for about $5-15. The hose barbs aren't 
always the size you'd like, but nylon adapters are cheap at the hardware 
store :-)

Might be easier to try making the CO2 diffuser less efficient first 
though... There are lots of ways to do this -- the idea is to reduce the 
area of the gas-water interface (making larger bubbles or fewer bubbles), 
and/or decreasing the contact time of the bubbles with the water (placing 
the diffuser closer to the surface, NOT using anything to keep the CO2 in 
the tank, etc.). Seems strange to be advising on ways to REDUCE CO2 
diffuser efficiency, but if you want less CO2 in your tank from a DIY setup 
it's probably the easiest way to do it.

     -Bill





*****************************
Waveform Technology
UNIX Systems Administrator

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