Fish dying?

nothing new added to th etank..
i am using a fluval 404 filter..
if a fish parasites and it dies will the other fish get the parasites.
 
My money is on lack of oxygen/co2 poisoning. Fish at the surface gasping is a sign of oxygen deficiancy. Your plants will use oxygen at night when the lights are off. A sign of this is if you always find fish dead in the morning. There is no way, I would keep that many fish without some surface agitation. Also, I have seen other threads started in this forum just like yours and the cause was figured to be the Co2. I would increase surface agitation and like Kas said, pull the Co2 until you can take accurate readings of Co2 levels. I wouldn't pump anything into my tank unless I could messure it. You may not even need Co2 with that many fish and a moderately planted tank. One other thing, maybe I missed it, what size is the tank? What are the demensions? Taller tanks don't have the surface area that longer tanks do for oxygen exchange.
 
O.k Lost another fish today morning.
MY sailfin lyertail white Molly.. my second fav fish :( RIP


my ph last nigh was 6.8 kh 7 so CO2 around 30ppm
my thank is 72 gal bowfront, you are right J. Morbett that i do not have enough surface area for O2 exchange, also i have NO surface agitation to reduce CO2 loss.
and also i the fish have been found dead in the morning.

So its pointing towards CO2

BUT if it was CO2 poisoning then how come all my fish are not dead?
Also if i add a air stone at night that will drive off the CO2, which will lead to PH swings.
Which i though was REAL BAD for the fish.
Plus one more thing every time a notice a fish hanging on the top gulping for air i find in dead in a couple of days.
The molly that dead today was healthy; eat well and swimming couple of days ago.
last night it was hanging by the surface too...

Please note i am a newbe to this Planted tank stuff. the plants were not doin to great so i add CO2 now they growing great. Plus the tank is moderate to heavily planted.
Light at 4*65watts for 10 hrs a day.

Please help. i dont any more fish deaths, it not fun.
 
the plants are growing great....so that means they're taking up more and more of the oxygen as they grow larger.

and different fish react differently. it may take time for the fish to experience the full effects of the lack of oxygen or poisoning. so if the CO2 and the lack of oxygen is the culprit, then your fish are slowly suffocating.
 
O.K. so i should add the air stone.
what about the PH swing from the Loss of CO2 at night..
 
Add the airstone and leave it on 24hrs a day. It will not lower your Ph much and if on 24hrs the swings in Ph from day to night will be the same as they are now with no air stone 24hrs a day. You could also use a power head pointed toward the surface (with or without air) to roil the surface. I've always been paranoid about my fish getting enough oxygen. I've always bought long and low tanks for more surface area. Right now I have a 72" long 125 with a powerhead in each corner and an 18 inch airstone in the back. Plus my filter return spraybar is angled toward the surface. And I'm relatively understocked. I have a few live plants that seem to be doing well in my tank, even with all of the surface agitation. You mention your lights and by my calculations, that's 3.6 watts per gallon. That's a lot of light. Your plants were not doing so well because they had the light, but not the Co2 for extreme growth. I'd say, cut 2 of the lights. Go for 2X65 in the 72g for 1.8 watts per gallon. Your plants won't require as much Co2 with less light. And now you can add surface agitation, which willl loose some Co2, but with the light cut, it should be a wash. The main thing is to get your fish some air....now.
 
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