Sudden Pond Fish Deaths
I have had an outdoor fish pond (150 gallons) for the last 4 years. I only have comet goldfish in my pond. I came home to find the 3 largest fish dead.
<<Marina here, I'm sorry to read this.>>
I have had them for the last 3-4 years. One of the larger fish was still alive but floating on his side and gulping for his breath.
<<In need of oxygen, possibly too much carbon dioxide or worse in the water.>>
I tried to save him, but was unsuccessful. I have 4 smaller comets that were their offspring (2 yrs old) that are still alive and they do not have any signs of sickness. I am puzzled as to why the larger fish have died.
I have never had any of the Comet fish to die. Our pump messed up and pumped about 70% of the water out the night before they died and we had to fill the pond up that morning. 
<<Oh man, there you have it my friend. This is how I lost a whole pond full of fishes once. >>
We were afraid that it would mess up while we were at work, so I did turn the pump off. 
<<Bad juju - you simply ensured that it would end up the same whether or not the pump "messed up".>>
The fish were fine before I left and seemed to enjoy the water change.
<<I'm sure they did, especially if it's been a long time since you've done any maintenance on the pond. A build up of mulm/detritus on the bottom would be another reason for sudden deaths - anaerobic conditions may very well have been created with such a buildup, the gasses then build to the point where they are released into the water et voila'! Dead, gasping fishes.>>
The outside temperature was around 73 degrees the day they died. I don't know if they died from lack of aeration, but I have left it off before without any problems. 
<<It wasn't that, it was such a large change without following aeration. For one thing, the water out of the tap has a great deal of gasses in solution. When you take that water out of the pipe, the pressure that kept the gasses in solution is gone, thusly, the gasses turn to bubbles, hopefully BEFORE the fish breathe them in. If not, they got the "bends" in a manner of speaking. NEVER refill a pond this way with fish and NOT ensure aeration and/or turbulent water movement to ensure this doesn't happen. Let's not forget that if on municipal water chloramine is likely present, bond between chlorine/ammonia MUST be broken chemically.>>
I have also done water changes greater than 70 % without any problems. 
<<Did you leave the pump off after doing such a large water change? In a situation such as this we cannot ascribe the deaths to any ONE cause, but more likely a chain of events, several root causes coming together for a lethal combination. Do some maintenance on the pond if it hasn't been done already, check the pump and replace if necessary. I LOVE Eponds.com by the way. Fantastic service, incredibly fast shipping, incredible deals on product.>>
Any ideas as to what happened to my large fish (10 -13 inches long)?
<<Whoa.. they got THAT big in just 3-4 years?? As above, a combination of factors is my best guess here. If you have plants then they help prevent these sorts of problems. If you don't, consider adding live plants. Marina>> 

Koi dead suddenly
Dear there,
<And there>
I have kept a 100 Gallon pond with 5 Koi for about nine months, the Koi is now about 7 to 9 inches,
<One hundred gallons? This is way too small a volume for this number of Koi of this size>
they have done well. the pond have filter and UV light system, half water change every two weeks.
<Sounds like a nice set-up, maintenance schedule>
But yesterday morning, they stop eating abnormally, and one dead afternoon. I was so surprised, tested water and changed about 2/3 water immediately. the water rate before water change is as, PH 8.1, Ammonia 0.25,
<pH is a bit high... is your tap water this alkaline? And the ammonia is hopefully just left over from the dead fish, and not something you have all the time>
Nitride 0, temperature 74.
Looked at the dead Koi, no any sign of disease, only have sticky skin, the left four looked have heavy breath, however they looked better after water change.
<Good move>
The nightmare is not finished, I found another dead Koi this morning, two of the three left fish have heavy breath again, I put this two weak Koi into an isolated basin with salted water and some medicine.
Can you image what's the problem I met according to my state, what can I do now to survive the lest life.
Thank you very much.
Bo
<Very likely what you are experiencing is more of a "seasonal" set of circumstances... the water warming up is increasing your fish's metabolisms and reciprocally is responsible for less solubility of oxygen... With such a small volume your fishes aren't getting enough oxygen... this is at least a major contributing factor to their distress, dying... I doubt if they have a pathogenic (bacterial, parasitic) problem... you can add some aeration, keep changing water frequently, but you really need a larger pond if you intend to keep Koi. Bob Fenner>

Goldfish behaviour 7/4/05
Hi
<Hello there>
I have a very large garden pond - twenty foot by forty plus foot, four feet plus deep at one side, lots of goldish which do breed and so on.  However they do this every year and I now feel I need to know why.
They are mostly just hanging suspended in the water, like they were asleep, although they did consent to eat a little yesterday and in the post dawn period they make little bubbles on the surface which linger most of the day.
<Ah, yes>
Can anyone tell me what they are doing and why?  No filter or oxygenator alas but I have lived here for more than ten years now and have managed so far okay.
Thanks very much
Angie Watts
<They are experiencing changes in the pond due to the season... in essence being poisoned... changes in pH, mixing of bottom water... You might consider adding aeration, biological filtration... that will make this system overall more homeostatic throughout the year. Bob Fenner>

Re: Pond Goldfish behaviour 7/5/05
Thanks very much for your reply.  I found the credit note from the water company when we had to have the concrete pond relined with a butyl liner as it had cracked (September 2003) and I found I reclaimed for 35metres3 not put back into the sewage system.
<A good note... in the States we also can at times realize such a saving from notifying our water/sewage service provider>
Add to that the contents of 2 x 45 gallon containers, one large fish tank and a paddling pool (for the marginals) I think that works out a pond approx 7,800 gallons, am I about right?  
<Mmm, 35 cubic meters of water is about 9,409 gallons...>
About a hundred goldfish (although most of them have bred black).  I have ordered a solar powered oxygenator to help things & use barley straw in old tights (last added about three weeks ago) but I guess 2 and half inches of rain the other day really upset my systems. Although I have to confess I was in there the week before taking out some weed!  At the moment I am just spraying the water a little each day to add oxygen.
<All good techniques>
The fish seem to be okay but after looking through your web site I am resolved to feed them less often than the several times a day they have got into the habit of begging for.
It's a great site - I have learnt so much from looking at it.
Cheers
Angie Watts
<Thank you for your kind words, caring and sharing your experiences. Bob Fenner>