Sounds like biogenic decalcification. The plants are stripping CO2 from the
hydrogen carbonates causing pH to rise and kH to crash. Yes, you need to
either supplement with CO2 quick and/or change 50% of your water to get rid
of some nutrients. In the meantime, turning off the lights will temporarily
stop the carnage.

Your tiger barb died of alkaline intoxification. Note that continuous
flucuating pH also can be harmful/deadly to your fish.

Bob A wrote in message
...
I planted (heavily) my 55g tank 3 days ago. I tested my water parameters
this morning (a tiger barb died, I don't know why) and my KH is 1 (or
less)
and my pH is 9 (from 7.2).

I need help quick. I am guessing that the plants are using the CO2
rapidly?

I added TMG when I planted, less than half dose (as recommended by the
instructions) but stopped after I was told I might need to hold off a
couple
weeks on fertilizer. I have a 1/3 flourite substrate. NO3 15ppm (same as
before I planted).

I guess I need to get some CO2 into the tank QUICK? I have brewers yeast
on
the way. Would it help to turn the lights off in the meantime? 110w
installed immediately after planting.

thanks so much,

bob allred