By Steve M. Meyer
Q. I have five koi that are just over three years old in a 130-gallon tank. Their sizes range from 12 to 24 inches. The tank is equipped with two power filters, one canister filter and two powerheads driving two submerged mechanical filters.
The fish are healthy and active, and both my wife and I enjoy them very much. The problem is obvious. They have outgrown the tank and they are still growing. They have already broken the pieces of glass on top of the tank many times due to their jumping, often when I was trying to change the water.
There is no possibility of my building a pond inside or outside the house, and a larger custom-made tank would have to be built on site because it would not be able to get through the entrance. I am looking for advice regarding a more efficient and low maintenance filtration system and any other suggestions for a way to cover the tank. We don't want to give the fish up.
A. I'm afraid you are not going to be happy with what I have to say. Despite all the best of intentions and technologies, there is simply no way you are going to keep those fish alive — let alone healthy and happy — in that 130 gallon tank for much longer. No amount of filtration, aeration, water changing and so on will matter.
Consider this. Suppose you had a free-flowing pond and stream system near your home. Imagine that the water from that natural source was absolutely pollution free, always kept at a temperature of around 70 degrees Fahrenheit, and was near the saturation point in dissolved oxygen concentration. And suppose you were able to pump 100 gallons per hour from the pond through your tank year round.
The fish would indeed survive for a while. But ultimately they would die from stress-induced disease. This is because there is more to maintaining a healthy aquatic environment than biofiltration, aeration and feeding. As koi mature they have a wide range of physical, biochemical and behavioral requirements that can only be met by "space."
Let's just assume that you have three 18-inch animals. If they are at all healthy then they probably weigh around 2¼ pounds each. So you have almost 7 pounds of fish in about 100 gallons of water (taking into account gravel, air space at the top, etc.).
For the sake of a rough approximation, assume that the fish have the same basic density as water. Because water weighs about 8 pounds per gallon, it follows that about 7 percent of the tank volume is taken up by fish!
Even in the most incredibly over-crowded fishponds — in which as a matter of routine catastrophic fish die-offs occur every several years — I have never seen a ratio exceeding 1 percent. (As regular readers know, my absolute maximum rule of thumb ratio is about 0.1 percent.)
Moreover, the configuration of the water volume matters. Even in the most ridiculously overloaded ponds the fish have the space to turn around freely and roam. If your tank is 24 inches wide, your largest koi has to struggle to change direction. Repeated physical contortions just to maintain some degree of motion will be fatal.
This magazine has used a lot of column space to discuss stress as a source of disease. I recommend you review these articles. You are holding these fish in conditions that will induce chronic stress of ever-increasing amounts. I urge you to take these fish to a local store or breeder and trade them in for three young (6-inch) koi. "Recycling" your koi is the only intelligent and humane option you have.
Advice That Works
Q. A few years ago I wrote to you regarding your suggested fish stocking levels. At that time I was relocating to Guam, and I will soon be heading back to the States. When I first got to Guam I bought two small ranchu and one lionhead.
About six months ago a new pet shop opened here. The owner — a nice, knowledgeable man from Singapore — and I have often had conversations about fish keeping, but he seemed not really interested in much that I had to say. In preparation for my move, he came to my apartment to pick up an old tank I was giving him. He looked in the goldfish tank, and I had never seen him so excited — so much so that he grabbed the telephone and called his wife.
He then asked me how I raised such beautiful fish (they were just pet shop fish) — he hadn't seen anything like them since he left home. Now, for the first time, I had his full attention. I described my fishkeeping practices and how I take your advice. He bought my goldfish.
A. Walter, letters such as yours are a big help. Readers should always take a "questioning" approach to advice they receive — even from experts. When readers report their experiences, it helps others to evaluate the value of what they are being told.
I would, of course, be just as happy to hear from readers who found the recommendations in this column to be completely out of touch with their experiences. I really do read all the mail and e-mail addressed to me.
Too Many?
Q. For about a month now, I have had a 30-gallon fish aquarium with a ryukin, a fantail and a small pleco. I have a power filter and an undergravel filter. Am I overcrowding the fish? I know about the nitrogen cycle and I am wondering how do the beneficial bacteria form in the beginning?
A. A given "volume" of fish will always grow better, look better, be healthier, and require less maintenance in a larger volume of water. So would a 60-gallon tank be better? Yes. Would a 125-gallon tank be even better? Absolutely! And a 1000-gallon would be better still.
But, of course, as hobbyists and breeders with real-life space, time and money constraints, we are often confronted with the situation of trying to do just enough for a good outcome. In this respect my answer is, no, I do not think you are "overcrowding" in terms of traditional aquarium practice or well-reasoned fishkeeping practice.
Of course, as the ryukin and fantail grow the tank will become overloaded. At that point you will have to upgrade their living situation or trade them in for smaller animals. But this will probably take a few years.
Get rid of the pleco now. It will cause serious problems for the goldfish as it matures. Exactly why plecos seem to victimize goldfish is not clear to me (I have never kept these fish together so I have no direct observations on which to theorize). Some have speculated that goldfish slime coats are too tempting for plecos to resist slurping. What I do know from reports all across the U.S. is that scale loss, physical damage and stress-induced disease in goldfish is far more common in tanks where they are forced to co-exist with plecos than in tanks where goldfish are kept by themselves.
Moreover, from the simple perspective of disease management, it is a bad idea to mix goldfish with tropical fish. The hosting of, and resistance to, various pathogens varies considerably between these two groups of fish, and keeping them together is asking for trouble.
The nitrifying bacteria (and other aquatic bacteria) that help to maintain acceptable water quality in aquariums are ever-present in the environment. And when the right conditions present themselves — water quality, oxygen (or lack of it in the case of anaerobic microbes), a substrate to attach to, and nutrients — these bacteria start to reproduce.
There are always nitrifying bacteria suspended in fish-rearing waters. However, there are too few of them in suspension (or on tank walls and ornaments) to process all the fish waste produced in the typical tank. The addition of a substrate, such as fine gravel or specialized filtration media, offers more growing room for the bacteria to occupy. The total number of bacteria in the tank increases 100-fold and more when a suitable substrate that offers enough living space is provided. Under such conditions the total bacteria population soon (within a month or two depending on water temperature) reaches numbers sufficient to handle fish waste loads.
Inoculating the tank with mature tank gravel or commercial bacteria products speeds the process by providing more breeding cells. It is still preferable, however, to completely cycle a tank (or pond) using ordinary, plain household ammonia for about 30 to 40 days prior to introducing any fish into the water.