Ponding is an endeavor of learning. As we go along, we pick up bits and pieces if information that we file away knowing that someday we'll need it. One problem I have consistently is being able to find the right bit of information when I need it. Also, one quickly learns that ponding is a life-science endeavor that encompasses physics, chemistry, biology, fluid mechanics, medical expertise, inspiration and perspiration.

In addition, I have discovered from questions asked me by people who have or are building ponds, that many wish not to be buried under reams and reams of technical information such as the specifics of the nitrogen cycle, but just want to know what to do to stay out of trouble until they can devote enough time later on to get into the specifics. Hence, the Pool Fool. (me) has come up with some do's, some don'ts, and some guidelines (without the technical reasons why) to follow to get started with your pool without making some serious mistakes.

Regarding the following recommendations about fish stocking limits, pool size, pump flow and filter size, all are done with a view towards safety, so a 24 hour power failure won't result in a pool full of dead fish. Any pool can be maintained in equilibrium without any filtration system at all by limiting fish population and feeding. By contrast, huge fish loads can be maintained in small pools if sufficient filtration and oxygenation systems are maintained in top operating condition. Neither situation is particularly desirable for most home water gardens. The Pool Fool's recommendations allow for a reasonable population of nice sized fish without the fear that even a 24 hour power interruption will result in a pool full of dead fish.

  1. Pool planning

    1. Always plan on the largest practicable pool for your yard, then double it. You'll wish you had if you don't.
    2. Always include water supply spigot at the pool filter location for automatic water level maintenance.
    3. Always include Ground Fault Interrupter electrical service via underground conduit to the pump.
    4. Take safety into consideration re: yours and neighborhood children ( best if you have a fence, regardless of pool depth).

  2. Pool construction (Liner pools)

    Some forethought to your filter system is in order before constructing your pool. Also, now is the time to decide on whether to include a bottom drain or side drain in your pool. The Pool Fool prefers gravity fed filters with water pumped back to the pool via a pump in the last stage of filteration. This requires the filter containers to be at a grade lower than the pool for the water to drain into the filter. If this is not practical, you will either have to place your pump in the pool (submerged) or in a sump constructed to allow the pump to be below water level so that it is automatically primed.
    1. Lay out your pool shape using garden hose to indicate water edge. Make sure the pool edge is level all the way around. If not level, you will have to do enough landscaping to achieve a level surface all the way around.
    2. Dig a 12" deep by 12" wide trench around the outside perimeter of the proposed pool.
    3. Line the trench with re-bar and pour full of concrete.
    4. After concrete cures, dig earth out of center.
    5. Dig pool with sides that slope no steeper that 80 degrees.
    6. Be sure that first ledge is at least 24 inches deep (to discourage raccoons/herons). Best depth for koi is 4 feet, but two feet is about average.
    7. Utilize "Fish Quality " EDPM liners only.
    8. Line the hole with old carpeting (tacks/staples removed).
    9. Do not trim the liner until after pool is filled.
    10. Cement stones or bricks, etc. over the liner on top of the concrete rim . Extend the coping stones over the edge of the water line to hide any liner above water level.
    11. If main (city) water is used, You must de-chlorinate before adding livestock.
    12. Save all leftover EDPM scraps to use in making bulkhead washers.

  3. Pool Size

    1. Estimate as closely as possible the square feet of surface area of your pool. (Width x Length = Area)
    2. Estimate as closely as possible the number of gallons of water in your pool. (Area {in feet} x depth {in feet}= Volume {in cubic feet}. Volume {in cubic feet} divided by 7.481 = Gallons) If you used a flow-meter or checked your water meter before and after filling you can use that result. Later, you will be able to confirm your total water volume via salt concentration measurement.

  4. Water Pump

    1. Pools up to 3,600 gallons are served most efficiently by magnetic drive pumps. Submersible pumps are generally easier to maintain and are quieter.
    2. Pools over 3,600 gallons are best served by in-line pumps outside of the pool or filter.
    3. Go to the Pool calculator POOL CALCULATOR and determine the flow volume and pipe sizes you will need. Then go to the head loss calculator HEAD LOSS CALCULATOR to determine the pump charactaistics you will need. One tip about head losses and plumbing: two 45 degree fittings always create less head loss than one 90 degree fitting.

  5. Filter system

    1. Generally, it is cheaper to build your own filter system. There are some very good commercial filters available, but they are relatively expensive and the good ones are not that common. If you purchase a system, install it according to instructions from the manufacturer. The most important commercial types are "Bead" filters and standard flow through type bio-filters.

    2. Your filter system ideally will have three components: A settling area, mechanical filtration, and a biological filtration section. Unless your are all thumbs, you should build your own filter because purchased filters are almost without exception too small and are always too expensive. If you have the resources, and inclination, bead filters can provide excellent filtration but the Pool Fool does not recommend them because of cost.

      1. Settling area- This can consist of a separate vessel into which the pool water first empties, or in an up flow filter, the bottom of the vessel. In any case each filter component should be fitted with a bottom drain equipped with a gate valve. Some knife gate valves are commonly used but not all are recommended for use in freezing weather. The settling vessel should contain a volume not less than one percent of the pool volume in gallons.

      2. Mechanical filtration-This includes any kind of batting, cellulose, or plastic mesh designed to remove solid particles from the water. The mechanical filter should always precede the biological filter. Mechanical filters ordinarily require frequent rinsing.The mechanical filter section should accommodate a filter area in square feet equal to your pump volume in gallons at 5 feet of head per hour times .0016667. For example, a 1200 gallon per hour pump flow times .0016667 would equal a mechanical filter area of 2 square feet. This equates to a circular area of a diameter of about 20 inches as a minimum recommended size. The pool calculator referenced above will calculate the size of your mechanical filter for you. You should construct a removable rack with handles to facilitate easy removal of the mechanical filter for rinsing.

      3. Biological filtration -This is the last and most important element of your filter. It processes the ammonia waste from the fish and uneaten food into plant food. The biological filter section should be sized according to pump flow in gallons per hour at five feet of head divided by 6. For example, 1,200 gallons per hour divided by 6 equals 200 gallons. This entire volume does not have to be within a single vessel, but can be in several series connected vessels. The idea is to size the biofilter so that water remains in contact with the biomedia for at least 10 minutes. At 1,200 GPH, gallons per minute equals 20. At 20 gallons per minute, you get a 200 gallon exchange in ten minutes, hence a 200 gallon filter capacity. You may get by with half this volume by reducing the fish load recommendation (dealt with later) by one half. The pool calculator above also gives you a size range in gallons for your biological filter.

      4. Oxygenation--In order for the biofilter to work, there must be enough oxygen dissolved in the water. Although you can use an airstone in the first vessel, The Pool FOOL prefers the following: For gravity fed bio-filters, incorporate a venturi into the first filter vessel fed by a small water pump in the last vessel. For pools with the pump submerged in the pool or external pumps located in sumps fed directly from the pool, utilize an oxygenation tower for the inlet to the filter system from the pump. This involves pumping the water about two feet higher before emptying into a large diameter pipe that extends to within 5 inches of the vessel bottom. The top of the pipe should extend above the inlet from the pump by 12 inches and remain uncovered.

    The above functional sections of your filter can be included in one vessel up to as many as practical. Three to five will usually suffice. There are many materials one can use for bio-filter mediums. The Pool Fool recommends you use agricultural tree netting (bird netting) as your bio-filter medium. Simply tie it in a ball and attach a nylon cord and stuff it into your container. It is light, has a large surface area, and is easy to clean. The best shape for a filter container is round, with a downward protruding cone shaped bottom, terminating in a drain controlled by a gate valve. This helps make filter maintenance easy. Many commercial filters employ this idea, but you can approximate the same result by troweling concrete into the bottom of your container 3" deep on one side and i" deep on the drain side or, if your drain is in the center, shape a downward cone out of concrete that terminates in the center. Be sure to reinforce the concrete with some chicken wire and seal it with DRYLOCK™ , and after curing, wash with vinegar. Any filter system, regardless of design is heavy. For this reason, the filter must rest on a firm foundation. The pool fool recommends a concrete slab.

    Miscellaneous tips:

    1. Gate valves and drains on filter containers should be no smaller than 1 1/2" PVC.
    2. In order to reduce pump inlet blockage, utilize the gavity feed of water into your filter and either submerge the pump in the last filter vessel or pipe the pump inlet out of the last container so that you are pumping filtered water.
    3. PVC pipe size recommendation for gravity flow:

      3501 1/2"

    4. PVC pipe size recommendation for pump output flow:

      7501 1/4"
      1,0501 1/2"

In plumbing the filter and pump, avoid as many angle fittings as possible, except that remember, as noted above, two 45 degree fittings present less friction than one 90 degree fitting.

Keep all water pump and return lines as short as possible.

Avoid unecessary bends in gravity feed lines.

If you are utilizing a multi-container filter system, consider installing a bypass line between the first and last vessels just above water level so that should the filter media become clogged while you are out of town, the pump can still operate.

A good idea is to make the connections between filter vessels out of hose large enough to fit over your bulkhead fittings, and secure them with hose clamps. This will come in handy should you ever have to move your filter.

Bulkhead fittings are available at some commercial outlets but you can make your own. Simply select male and female treaded PVC fittings of the size you need and cut rubber washers out of your EDPM scraps. If your vessels are thin walled (like trash cans,) you need to carefully cut about a 3/4 inch slice off the threaded end of the female fitting to use as the nut on the male fitting. Otherwise, the fittings may not screw together close enough to seal the washers.

  • Fish load

    There is probably no other aspect of koi keeping more in dispute in the United States than how to measure and maintain your "fish load", and what should it be?

    This problem has many approaches, such as "inches of fish per gallon", "inches of fish per square foot of pond surface area", "pounds of fish per gallon", "pounds of fish per square foot of surface area", and "surface area of the fish to gallons of water".

    Using various sources on the WWW, I assumed a pool of 15 feet by 10 feet (150 square feet) by 2 feet deep (2,244 gallons) and calculated the pounds of fish that would result from using the recommendations of these sources.. Fish size is assumed to be 12 inches for all fish in the pool.

    1. Aquatics Unlimited

    (1- 12 inch fish for every two square feet)

    Their recommendation for the example pool converts to 75 pounds of fish.

    2. Aquaria glossary

    ( 1 inch of fish for every gallon of water.)

    Their rule applied to the example converts to 187 pounds of fish.

    3. Purdue University Cooperative Extension Service

    (10,000 pound of fish per acre.)

    Number of pounds of fish for the example pool: 34 lbs.

    4. Aquarium Fish Home Page: Fish Library Page

    ( 1 1/2 inch fish per 10 square feet of surface.)

    Total pounds of fish recommended for our example pool using this rule: 15 pounds.

    5. Reliable Garden and Fence

    (2 inches of fish for every square foot of surface.)

    Conversion to pounds of fish for the example pool: 25 pounds.

    6. The University of Georgia College of Agricultural & Environmental Sciences Cooperative Extension Service

    (1/2 inch per every 3-5 gallons of water or square foot)

    This recommendation gives a range of from 12.5 pounds to 31 pounds.

    As you can see, with a range of 12.5 to 187 pounds for a 300 square foot 2 foot deep pool, this can be most confusing. Inasmuch as the aquaculture industry uses "pounds of fish per square feet surface area" almost exclusivly, I decided that a pounds per square feet method would give the most useful data and performance over the long run. The tricky part is that fish metabolism changes according to environment and fish weight is not directly proportional to length (the easiest measure). One could, of course, actually weigh your fish, but you most likely will stress both yourself and you fish unecessarily in that endeavor. Because of this I developed my Fish Load Calculator for my own use and decided to share it with you for whatever it may be worth. The calculator contains conversions from length to pounds for various sizes of fish. Fish less than two inches may be ignored. Remember, I said I'd try to keep it simple. These recommendations assume you pay ordinary attention to water quality re: ammonia/nitrites/nitrates, etc.

    In my opinion, most fish lost from too heavy a fish load are lost because the surface area of the water available to them is deficient as compared with their need for oxygen. If you stock your pool with a view to safety as regards power outages in the heat of the summer, you may well save yourself coming home to a pool full of dead fish. Remember, when Koi expire from lack of oxygen, it's the biggest ones that die first.


    Last modified on March 13,2000

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