Dave, on your small tank you might consider 2 one liter bottles rather than
one 2 liter bottles, changing the solution in one of them each week. Join them
together with a brass "T". Also, the glue seal won't last forever. One way to
keep the seal tight for a longer period of time is to install a quick
disconnect. They're tiny and terrific. The great feature is one side will
valve shut when they're disconnected. If that side is upstream (toward your
filter system) this prevents losing CO2 from the second bottle and also
prevents O2 going into that bottle - and it reduces stress on the silicon glue
seal. You might also want to unscrew the bottle from under the cap as opposed
to unscrewing the cap off the bottle. I think the quick disconnects can be
purchased through MarineMonsters and/or Florida Driftwood or...