Q. We built a 6000-gallon pond a few years ago. It is well-planted and we keep about a dozen koi. This is a liner pond. We circulate water with a 1600-gallon-per-hour sump pump that sits at the deep end of the pond. The outflow hose from the pump runs along the pond floor, up the side (underneath some rocks) and then to the top of a waterfall.

Our problem is that the sump pump is always clogging with leaves and other debris. We have to clean out that pump every day to keep the water flowing. Changing the size of the filter screen does not seem to matter. What can we do to reduce the maintenance?

A. This is a common problem in well-landscaped ponds with very-high-flow-rate submersible pumping systems. The suction from the pump is so great that it draws in debris from across the pond floor, quickly clogging the works.

A partial solution is to manually clear the pond floor using a swimming pool leaf-raking net on a long extension pole to remove as much of the material as possible. This probably needs to be done only a few times in the early spring and late fall. This procedure will undoubtedly cloud the water with all kinds of temporarily suspended matter. So it might also be a good time to do a 30-percent or greater water change. Pump out the cloudy water first, then refill. The koi will not mind the temporary mess.

You might also think about installing a higher capacity in-pond mechanical filter screen for your pump. There are many ways to do this, so let me suggest a simple and inexpensive version, and you can improvise. Purchase a plastic hamper with grilled sides at any department store. Place some large stones in the bottom and submerge the hamper in your pond. Now place the submersible pump inside the hamper, resting on the stones. That's it.

This approach has two drawbacks. First, a plastic hamper sitting in your pond will be a less-than-attractive feature, so you may want to think about ways to hide or disguise it. For example, plants (such as water lilies or water hyacinths, or a tall stand of cattails) and ceramic water features can be used as a screen.

Second, extensive removal of the leaf litter and debris sitting on the pond floor will destroy much of the pond's natural value for aquatic invertebrates. Dragonfly larvae, caddisfly larvae, a host of beetles, snails, and tons of other near-microscopic critters live down there and are very beneficial to pond ecology. Not the least of which is the fact that they are food for small fish.

An alternative, then, is to move the entire pumping system outside the pond to an external basin. Although it does represent a bit more work than my earlier suggestion, the maintenance and operation benefits are substantial, as are the aesthetics.

The external basin can be any size — from a standard 32-gallon rubber trash pail to a 150-gallon PVC horse trough, or even larger. It should be situated within a few feet of the pond and sunk into the ground so that the top of the basin is just an inch or so above the water level of the pond.

If you are worried about jeopardizing the integrity of the pond liner, the basin can be connected hydraulically to the pond by a large (in your case, 3-inch) siphon tube make from PVC pipe. This definitely works, but it is awkward and unsightly (again, there are ingenious methods for hiding the siphon pipe with plants, etc.).

Alternatively, you can connect the pond and basin with an underground pipe. You will need a special liner fitting to connect the pipe, and a bulkhead fitting to put through the basin wall. If you cannot find a 3-inch fitting you can use four 1½-inch pipes to get the same basic volume and flow. I would pierce the pond wall at mid-level, not at the bottom. You do not want to disturb the floor too much.

Now place your hamper/pump inside the basin and you are set to go. Turning on the pump draws water into the basin, where accompanying leaves and other debris are trapped. Occasional cleaning involves nothing more than shutting off the pump, removing the hamper/pump and scooping out the gunk.

Fade to Black
Q. Help! I bought three fantails a month ago and they started turning black. First it was their tails, then around their heads. The guy at the pet store said it sounded like fin rot and sold me some antibiotics to add to the water. It did not work. The fish are almost entirely black! What disease is this and what can I do?

A. There is nothing you can do. The fish are not sick, they are just changing color. There is a form of fin rot that blackens the finnage of fish — this is the dead tissue. But if the problem really was bacterial infection your fish would be long dead.

The guy at the pet store made his best guess based on what you told him. Chances are had you brought the fish in he would have recognized the simple color change.

Color change is quite common in goldfish and koi. I just had what was a beautiful showa (a black koi with broad red and white markings) transform herself into a beautiful black and white utsuri (a black koi with broad white bands). After 10 years of being a showa her reds just disappeared, to be replaced by pearly white. Pretty remarkable.

Such changes may be caused by environmental factors (e.g., changes in water quality, sunlight, etc.), age or food. Enjoy your black goldfish. Keep them in bright light and they will develop a nice rich velvety black color.

They Eat, They Don't
Q. Last year I installed a small backyard pond that holds about 1300 gallons. It is only a foot deep, which is fine for our area because it never gets cold enough to freeze. I keep a dozen or so fancy goldfish and three medium-size koi in the pond.

My question involves feeding. This past spring my fish ate like crazy. They couldn't get enough food. I must have been out there eight times a day dumping pellets in the water (making sure that they finished everything within 10 minutes). Now, they barely eat all the food at just two feedings a day. I am worried that they are sick. Because it is so much warmer now, I figured they would be eating even more! A friend who raises tropical fish suggested they may have an internal infection and that I should treat with an antibiotic. Any help you can offer would be greatly appreciated.

A. Hold off on the antibiotics, Bob. You would be wasting your money and endangering your fish.

The first thing to consider in changed eating behavior is water quality. If the fish were eating like crazy and suddenly have cut back, there could be a problem with pH, dissolved oxygen, ammonia or nitrite. Test the water immediately.

Why would the problem crop up now? As the water warms and nitrification accelerates, so does the acidification of the water. If your fish were eating as much as you say, the nitrification could have significantly lowered the water's pH. Once it gets below 6.5 or so the fish may not feel so healthy or hungry.

Higher air and water temperatures mean lower concentrations of dissolved oxygen in the water. Feeding fish consume much more oxygen per minute than inactive fish. If oxygen levels are below 5 parts per million (ppm) consider additional aeration via a fountain, a waterfall or a bubble aerator.

The feeding frenzy earlier in the year may have corresponded to a growth surge in the fish, and now you simply have too much fish waste (and excess food) going into the water. In other words, the fish load is much larger than six months ago. (Because you didn't mention anything about pond filtration, I can only guess that you may not have adequate biological filtration.) If you do have measurable quantities of ammonia or nitrite present, a 50-percent water change is in order. You should then use an ammonia remover, or add 1 pound of salt per 200 gallons of water, to mitigate the nitrite poisoning. A more permanent solution will require a pond filter — or fewer fish.

Of course, it may well be none of the above. Pond fish eat excessively in the spring because they go on a starvation diet during the winter (even in your area). They may lose 20 percent or more of body weight during the winter.

When spring comes and breeding season approaches, they start to pack in the food. So, what you saw in the spring may have been a seasonal anomaly. As the weather warms and breeding season passes, goldfish and koi cut back on feeding. I notice this clearly every year in my fish.

Then, too, by mid summer algae and other natural pond foods become available and so the fish eat even when pellets are not available. If all the fish are feeding and they act healthy, then you are probably just observing a natural cycle. As you gain more experience with the fish these things will become second nature to you.