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[APD] water change and pearling

Hi everyone,

lightly green newbie here.  I'm reading the responses to Tom Barr's  
posts and have 2 additions.  First, something I didn't know that I  
don't think was in Tom's post: the CO2 concentration in air is about  
300 ppm, gleaned from a very limited number of web pages found by way  
of Google.  That's way more than I have in my tank.  Second, is there  
something in the water that is inhibiting plant photosynthesis and  
hence pearling?

My own experiences:  I have had a tank for about 6 weeks and am  
reading and monitoring my tank.  I have done small water changes but  
did a larger water change last week and saw pearling on basically all  
my plants.  Made me wonder why.  When I did the water change, I added  
ferts that Tom gave me.  a couple days pater, I added NO3 and got no  
pearling,  Next day, I added PO4 and got no pearling, so they're not  
the reason.  I removed a few snails with as siphon hose and added a  
couple gallons of fresh water (to a 55 g tank) and again got some  
pearling.  The water level was barely down, certainly not enough to  
give air exposure to the plant leaves (IMO).  Still wondering about  
the water change thing.  I'm not arguing that water changes are bad,  
but more why are they so good?

I work in a lab in the med school at Davis.  Growing mammalian cells,  
we add lots of goodies to keep them happy and kill bacteria.   
Sometimes, we use old media from some cells mixed with fresh media to  
keep the cells growing.  Such media is called "conditioned".  The  
original cells added growth factors and unidentified goodies to the  
media to help stimulate sensitive cells to grow.

So, in a like fashion, do plants give off things that build up and  
slow their own growth?  Maybe an experiment to perform is remove tank  
water and save it for a day or a week (measure CO2 when removed and  
when added) and add it to a tank as fresh water and see if pearling  


John F. Hess, Davis California   johnfhess at comcast_net

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