My Fish Died!!!!!!!!

I added a bunch of plants to my tank yesterday evening, performed a 40% water change, added Flourish, flourish trace, and flourish excel at the recommended dosages. I also added a small powerhead, and reduced the surface agitation of my spray-bar. When I got up this morning my two pictus cats were stiff as boards and just as dead! I tested the water and this is what I have:

before the additions-PH 7.4-6 Nitrate 5 ,gh 5.6 dhdegrees, KH 2.4 degrees

after_- PH 7.2 NO3 5, Phosphate 0, KH 2.24, Ammonia 0 , NO2 0
calcium is 20ppm, Iron is reading at 0 (chelated and non-chelated).

Any Ideas? The rest of the fish appear fine, even the Ottos.
TIA

No, I only added one dose. The only fish affected were my catfish. I think that when I did a water change my tap water has a lot of co2 and then when I added the excel..well you get the idea. On a brighter note, I put all of the Head and Tail lights from my ten into my 72 last night. Today they are spawning like crazy, I have three females and three males, and all of the females are spawning. On the sad side, the Serpae are being well fed today .

Thanks for replying, .

Nothing else has died and I did a 20% water change, so I am hoping that everything is o.k.. My water is a little cloudy now though. It may be from getting it so stirred up when I planted all of my new plants.

Thanks for all of the ideas. The excel says to put one capfull for every ten gallons at startup and at major water changes and I think I only put half of that. I am only putting it in every other day now (the dropper's 5ml).


Some lessons are painful to learn, next time I will do more reading up on what I put in.

RICHER- I am pretty sure I disturbed the substrate a lot, I put lots of plants in and moved a really large piece of driftwood. Plus the laterite had only been in about a week, it still kicks up dust if it gets disturbed even though it is mixed in with the gravel.

JASON B- The bottle says One capful (5mL) for every 80L(20 gallons) twice a week. I put in 3 capfulls for my 72 gallons on Friday, the day I planted, along with Flourish and Flourish excel.
Does Flourish have the same things in it as Flourish Trace? I added just at one half capful of the Flourish--it says one capful for 125 gallons twice a week.

Also, what else should I be adding? My iron reads 0, and phosphate reads 0 or.25 at the most. NO3 (when I can get the drops to come out) also read 5 at most.

I am getting so confused...Hopefully plants will live and so will the rest of the fish.