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RE: air at night
I use an airstone at night in my CO2-injected tank. This adds O2, mostly
via surface turbulence, and drives off much of the CO2. Here are the pros
and cons of this approach as I see them:
PRO: Fish never suffer from oxygen deprivation. Fish seem healthier and
CON: Expense (air pump and timer). Noise (air pump and diffuser). CO2 is
driven off and wasted. The loss of CO2 causes a pH increase that may stress
I think this is a controversial practice; many people say that with healthy
plants you never need to worry about oxygen. I've found this to be true,
but with a major exception: if anything goes wrong with the plants, the
fish can suffer due to lack of O2. A major water change, an algae or
nutrient problem, a major pruning can all cause this to happen the next
night. Also, if your aquarium has a high fish load or less than a "Dutch"
amount of plants, it can happen regularly.
All I know is, the pH swing due to the loss of CO2 is minimal and gradual,
and I've never had any fish stress or deaths due to pH swings. I *have* had
fish stress and deaths due to O2 starvation, sometimes even when the plants
were bubbling like
crazy the day before. I haven't lost a single fish in the 2-3 months I've
been running the airstone at night.
If you're considering this, try watching your fish at 1:00 am for a few
days. In my case, even when the plants were bubbling like airstones, the
fish would all gather at the surface gasping for air a few hours after the
lights went off. This usually didn't kill them, but it was stressful and I
would occasionally lose a fish--and always a fast-moving fish that needed
high oxygen levels.
I suspect this is mainly a problem that those of us with relatively high
fish loads run into. I like to keep my one inch per gallon of fish, or a
bit more, even in a planted tank. Amano's fish loads tend to be a bit high
and some of his designs use a relatively small number of plants, so I'm not
surprised that he does this too.
Injecting *pure* O2 is a novel idea; I imagine this could be done silently
and, with a good diffuser, wouldn't drive off CO2. However, this would be
expensive. More importantly, my aquaria are definitely NOT worth the risk
of keeping a canister of pure O2 in the house...
michael moncur mgm at starlingtech_com http://www.starlingtech.com/
"Let's have some new cliches." -- Samuel Goldwyn