The Tale Of 9 Dead Goldfish. Importance of Water Quality

Last summer my family and I went to the USA on holiday for 3 weeks. This was not unusual since we go away typically for about 8 weeks every year. This time it was different ... our pet goldfish in our small garden fish pond all died one night.

We live in what is called a cluster complex ... houses grouped together with a single central security controlled entrance. This type of house normally has limited garden space. Despite this we installed a small fish pond about 7 years ago using a black plastic preformed liner. The pond was about 3 feet deep and held about 380 litres of water (about 100 gallons). When this small garden pond pond was installed we did all the right things and it was always a pleasure and there were few hassles over the years ...

• We had 2 pumps to make sure the pond filter was able to get running water 24/7 and were able to still switch off the waterfall when not needed. We did this to save electricity.

• We installed a biofilter and UV light system to control suspended algae so we didn't get cloudy green water in warm weather

• We installed a number of pond plants to help remove nitrates

• We never had to add any chemicals throughout the whole life of the pond.

• The water was always clean and crystal clear

We started with 4 very small (between 1 and 2 inches long) goldfish. The fish grew and every year for the last 4 years or so there was always frantic breeding activity marked by our seeing small black "goldfish" appear as from nowhere when they were about 3/4 inches long. Of course what had been happening was that the eggs were being eaten as soon as they were spawned. However one or two brave (in fact 5 in total) goldfish survived I presume by hiding in the plants only to reappear when big enough not to be eaten any more. These young fish were almost impossible to see because they were not gold ... they were in fact always black, They only started to become gold at about 6 months of age ... in fact one became white.

So this small pond was a treasure and the fish were all named. They were fed every day and became very tame and they obviously enjoyed their watery home. They survived quite happily despite tropical thunderstorms, hot summers, cold winters, muddy waters from excessive rain, and visits by bird predators. By the time of the incident the largest was about 9 inches long.

Goldfish are far more hardy and easier to keep than larger sized koi.

We had been on holiday about 3 days and then got a frantic message that all the fish in the pond were found floating on the surface. My office staff quickly got a local koi expert to take a look and the verdict was that there was nothing obviously wrong that could be identified.

To this day I do not know why the goldfish died and so I presume because it was a mass death and happened overnight and in summer that lack of oxygen (or maybe ammonia poisoning) was the probable cause ... but what caused this I don't know. The pumps were running although the waterfall pump had been switched off as it was every night so this in itself was not unusual. And the biofilter UVC combo was working too.

Why I say night was a factor is that during the night plants take oxygen out of the water (during the day they add oxygen to the water). It is possible that therefore that oxygen levels dropped to a level too low to sustain life ...  although I can't help but think in this circumstance maybe a few of the goldfish would have survived. As fish died there would be a little bit more oxygen for the ones left behind.

There were no signs whatsoever of any disease and such a sudden mass death is not typical of disease or infections anyway.

So yes in mind suffocation was the probable cause of our pet goldfish dying.

The lesson if there is one at all is that our ponds hold life and they are completely dependent upon us for that life. We are holding them in an unnatural environment which means our equipment has to be in top working order at all times ... it's a sad story.

We still wonder what would have happened if we had not been away on holiday.

Read about ponds and oxygen here Water Circulation | Pond Filters Needs Oxygen To Work