Koi Fish Information Centre

A 25-30G mini-pond isn’t very much for outdoor use. The water will be subject to drastic temperature swings that a larger volume would be better able to handle.
If you had a plant like a palm or other thick crowned plant, you could have one or more of them next to the “pond” to provide shade from the sun but since the actual temperature swings during the day/night are usually around 20F, that’s too much for most fish to handle.
What kind of fish were you considering? Oops.. I just saw you were considering butterfly koi. They get far too large (30″+)_ for your proposed pond. Long-bodied goldfish (12″+) need a minimum 50-100G each and Koi need a minimum of 500G each for long term success. Even round-bodied goldfish need lots of water volume (30G+ each) since their body mass is the same as their long-bodied counterparts. So you might have to go with other hardy fish like zebra danios, WCMM’s, etc., which can handle colder water down into the 60’s-70’s and can handle tropical temps up into the low 80’s so you’ll at least have to make sure the temp stays in that range but you might want to add a heater set at the mid 70’s to keep the total temperature swing down from day to night. The heater would only kick on when it gets cooler (at night or during cool fronts).
I can’t think of the name of the fish off-hand but someone mentioned a smaller tropical fish that resembles a goldfish and if that fish is capable of handling the temperatures, you might be able to keep them since you seem to like the look of goldfish/koi. Hopefully, they’ll see this and reply with the species again.
They also have the genetically engineered Zebra Danio’s called Glo-Fish which have day-glo like coloring in their genes.
Throw in a lot of fast growing easy to grow plants (one that I like is Anacharis which can be planted or can be left floating on the surface which would provide some more shade/protection to the water/fish). The plants will also help with the overall ecology of the “pond”.
Definitely use the powerhead to provide lots of surface agitation which will allow for better in-gasing of O2 into the water when it gets warm since warm/hot water does not hold O2 or other gases very well.
The other thing you could do is put your air pump inside your home so it’s pumping cooler air into the “pond” (instead of the outside warmer air) which will help keep the water from getting too hot during the warmest parts of the day.
This may or may not work for the fish so be prepared to either go with something bigger or be prepared to move the fish indoors… especially once the winter comes.
Lenny Vasbinder Fish Blog - http://GoldLenny.blogspot.com

Category: Philippines Internet Koi Society