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Re: What's missing?

On Tue, 14 Mar 2000, Chuck Gadd wrote:

> While doing this weekends water change, I once again observed MASSIVE
> pearling after the water change.

This is fairly commonly observed.

The easiest explanation is that your tank water before the water change is
undersaturated or just marginally saturated with oxygen, and the tap water
your changing with is thoroughly charged with oxygen.  With the plants
already photosynthesizing, the water change then leads immediately to
heavy pearling because the oxygen produced by the plants can't be
dissolved in the water.

Your Denver-area water systems get water from the man-made reservoirs all
over the area and the water is cold this time of year.  Cold water holds
quite a bit of oxygen.  When that water is piped through the system
underground it warms up and the warmer water doesn't (at least happily)
contain as much oxygen as the warm water.  Being sealed inside a pipe
though, the extra oxygen can't escape.

Small holes in pressured water lines can also cause supersaturation, by
aspirating air into the moving water.

You should be able to test this by doing your water change with the lights
out, and leaving them out for several hours afterwords so that the new
water balances out with the air.  After your lights come on there
shouldn't be any unusual bubbling.

Another tell-tale sign would be if the plants only bubble till lights out
after your water change, then you get only normal bubbling the next day.

Also, you should see much less of an effect like this in the summer than
in winter, because the reservoirs are warmer, and their oxygen content is

I doubt that any nutrient shortages could cause this short-term temporary
bubbling.  The nutrients don't have a direct effect on the photosynthesis
rate.  To the extent that other nutrients might increase that
photosynthesis rate it would be only after the plant had time to take them
up and build the proteins and enzymes that need those nutrients.  That
would definitely not be an immediate, short-term effect.

Roger Miller