I have three lovely ranchus living in a 15-gallon aquarium. They have gotten large, but have lost a lot of their color. I would like to put them outside in a larger amount of water, but am not really ready to build a pond.
A local nursery has plastic half- barrels that they are selling for container water gardening. They hold around 30 gallons. Would these be safe for keeping our goldfish outdoors? Would I need a filter?
I haven’t really said much about container water gardens in this column over the years, which is a unfortunate because they are a very versatile alternative to aquariums and ornamental garden ponds.
Container water gardens are usually between 20 and 150 gallons, although I have seen smaller and larger examples. Like an aquarium, they can be set up in an afternoon without any of the laborious digging a pond requires.
Besides the many commercial products available I have seen container water gardens that used converted horse troughs, old claw-footed bathtubs, half whiskey barrels and wash tubs. Anything that can be made to hold water can become a container water garden. Just make sure the container has been cleaned thoroughly to remove potentially toxic chemicals.
The simplest setup excludes fish entirely. Put the container in a sunny location, place soil (or pots) on the bottom and fill with water. Presto! A water garden lives. There are many flowering wetlands plants to choose from, and even some water lilies that thrive in these containers.
Of course, this standing water source becomes an attractive breeding ground for mosquitoes. That usually leads folks to add a few goldfish. Problem is goldfish do not really do a good job eating mosquito larvae, especially if the fish are well fed with fish food. In warm climates — and especially during the summer — tropical fish do amazingly well in container water gardens. And some are voracious mosquito eaters.
A container water garden can be a fine home for your ranchus if you take a few precautions. First, I would not keep the container in a location that gets more than an hour or two of direct morning or late afternoon sunlight because the water can get very hot. Find a location that shades the container from 11 a.m. to 3 p.m.
Second, fish in a container water garden are easy pickings for cats and raccoons. There is really not much you can do about this, but it is a consideration in designing and placing the water garden.
Third, whether or not you need a filter will depend on many specifics. Soil and gravel on the container floor should provide more than enough space for nitrifying bacteria. One or two fish in a 30-gallon container with a gravel floor and good plantings should be fine without a biological filter.
Proper aeration may be a problem. Sometimes a simple bubbler can keep dissolved oxygen levels high (and CO2 levels low). Or a small pump may be needed to maintain circulation. (Circulation also has the added benefit of discouraging mosquito breeding; they prefer still water.) However, too much turbulence in a container water garden can inhibit plant growth (especially water lilies) and stress the fish. The flow rate should be one-half to one container volume per hour.
Lastly, do not overfeed! Polluting the water with food and fish waste will lead to very rapid water quality degradation. The container water garden is more like a fish tank than a pond in terms of its ability to forgive overfeeding mistakes.