glenner003 wrote:
Neil Woodman" wrote in message

...

Hi,

If wonder if any of you guys could help me. I did my usual 30% water change

on Saturday night, I got in on sunday to find all of my tetras swimming
near the surface gasping for air, the only thing I had done differently was
increase the CO2 slightly. Then I noticed some bleeding heart tetras were
dead, and then I noticed some shrimp going a bit strange darting up to the

surface and back down again. Suddenly all the fish started to die in front

of my eyes! There was obviously no oxygen in the water so I added a
powerhead to create some surface agitation and did a 50% water change. The
tank has now gone really cloudy and I've lost most of my tetras and shrimp,
there are only some ottos, a 4 tetras, a rabble of shrimp and one ram which
is hard as nails left alive. So this morning I rushed to my local aquatic
shop. He asked me if the water had gone cloudy after I explained what
happened and it had, so he then said it was a breakdown in the filter which
has caused all the bacteria to go into the water, which had in turn
suffocated all the fish, he recommended doing a big water change which I had
already done and recommended I use some filter aid to clump together the
particles to filter them out faster, I cant remember exactly what he said
but it was along those lines. Can you guys explain what might have happened
and why? This has never happened to me before and I've been keeping fish
for a long time, to suddenly see them dying in front of my eyes has been a

harrowing experience.

I use an external filter and pressurised CO2, I dont know if that's

anything to do with it, the tank is heavily planted.

Thanks,

Neil



Hello Neil,

AFAIK An increase of CO2 implies a decrease of oxigen.

"Is It Possible to Overdose With CO2? Will My Fish Suffocate?

It is not likely that you will overdose the tank with a DIY system. It
just doesn't produce that much CO2. However, it is wise to monitor the
pH and the reactions of the fish for the first few days. If the pH drops
too low, you may not have enough buffering or you may be providing too
much CO2 for the size of your tank. The plants should produce enough
oxygen to provide plenty for your fish. However, if you should notice
them gasping at the surface, particularly in the morning, the oxygen may
have been depleted overnight and you will be wise to add an airstone at
night to aerate the water. This is rarely necessary, but do monitor for
it at first. Early morning is the best time to check for pH changes, as
it will be at its lowest at this time. Note: CO2 does NOT displace O2
and cause suffocation. The two concentrations are independent of one
another."

http://www.tropicalfishcentre.co.uk/Diyco2.htm

Nikki