Too much CO2

Hi everyone,

This morning when I was feeding my fish in my 25 gal tank and I noticed
they were all hovering around the surface, especially the ones that
normally burrow in the gravel (kuhli loach & fire-eel).  My clown loach
was just lying on its side on the surface & I was able to catch it and
put it in another tank (usually it's too fast to catch, as were the
kuhli loach & eel), it recovered & became active again in the other tank.

I measured nitrites & they were zero.  I measured CO2 & it was over 40ppm!
I removed the DIY CO2 apparatus (it was an old bottle that was almost
exhausted & was due for a change - I have not put a new one on!) & did
some water changes till I got CO2 down to below 30ppm.  The CO2 in this
tank is usually around 20 ppm when a new bottle of yeast+sugar is added.

The only new changes to the tank were the addition of an aponogeton plant
that I thought had gotten too big in one of my 10 gal tanks and a 10%
water change on Sunday.  The filters are running just fine & I have
lowered the water level to get more aeration from the two aquaclear 150
filters.  This tank already had another similarly sized (very large!)
aponogeton plant in it (with 6-8 3"x10" leaves).

The only thing that I can think of is that the aponogeton (elongatus I think)
puts put a lot of CO2 at night.  I was wondering if anyone new if certain
plants respire more - I'm thinking that possible this one does cause it
grows so rapidly & I'm wondering if anyone else has had similar problems.


P.S. regarding the plants that can withstand clown loaches: I have found
no problems due to clown loaches - what kind of problems have others had?

P.P.S. For the person who had white worms & other critters in their tank,
I had heard these problems often come about due to overfeeding which is
why you often see them in fry-raising tanks.