Lost all my shrimp last night!!

[WhiskeyD]

I went to go feed my fish this morning and I noticed both of my bamboo shrimp were dead! Upon further inspection, I noticed i lost all my Amano shrimp and every fish in the tank was at the surface gasping for air. Yesterday, I removed the last bit of porous rock from the tank and replaced it with driftwood. I knew the porous rocks (2 pieces, about 3" tall and 6" wide) were upping my PH so when I removed the rocks I did a 40% water change. The PH was about 7.0 last night and it had dropped to 6.5-6.6 today(same as my other tanks now). The Amano shrimps organs were red but the bamboo shrimps had normal coloring. I'm thinking the PH drop caused the shrimp to die but what about the lack of oxygen in the tank? I wouldn't think removing a couple rocks and cleaning the filter pads would cause a lack of oxygen could it? Any ideas what could have cause all of this?

I ran an air stone for 30 minutes this morning and all the fish have returned to their normal behavior. I'm really bummed out about the bamboo shrimp because I have had them for quite some time and watched them grow from about 1.5" to ~3.5"

Tank is a heavily planted 55G with a rena xp3, no co2 but i do dose excel. Ammonia and Nitrites are 0.



Edit - I found one Amano shrimp still alive! So i lost 3 out of 4

 

[mgamer20o0]

excel can cause the o2 levels to drop. maybe the switched blocked some of the surface agitation so the o2 dropped or moving things around kicked up some dirt causing ammonia/nitrite spike.

 

[jsoong]

Possibly a transient nitrite spike. Moving things might have stirred things up, and the rocks might contain a lot of your bacteria colony (porous rock has lost of surface area), so removing them (plus cleaning the filter pads at the same time) might have caused a mini cycle.

Nitrites binds to hemoglobin & prevent its uptake of oxygen. The fish would behave as if they are lacking O2, even if the water is not.