CWIC (Constant Water Inflow Change)
CWIC Constant Water Inflow Change Water changes can be a total pain. They're also a little stressful to the fish if they cause any sort of thirty-percent-magnitude fluctuations in temperature (~20 degrees) and pH (~two points). You also deplete some of the water's mysterious organic "mojo" with major water changes, and this upsets the 'feel' of the water to the fish.

HOWEVER - replacing water in the pond IS ESSENTIAL overall, because of some simple facts.... When solids are trapped in the gravel (ewww?) (not really) there are organisms in the gravel called: nematodes, rotifers, mollusks, worms, crustaceans, and even Koi who keep the mulm layer broken up and breaking down. There are also (important) beneficial bacteria which break down the chemical and solid wastes there. So, the stuff isn't just laying there, "decaying".....It's in a dynamic state of breakdown just like in natural soil outside your window, a healthy natural process.

Uhhhh, as long as the byproducts are removed naturally, or by YOU!

Well-l-l-llll the ponds' gunky stuff gets broken down into:

  1. carbon dioxide
  2. nitrate
  3. phosphate
  4. dissolved organic compounds. (DOC)

Plants and algae [if present] will use A LOT of this stuff, but plants and algae themselves produce carbon dioxide (at night) and a variety of things which also contribute to a climbing DOC level. Eventually, let's face it, DOC and phosphates, and nitrates, can get built up to a level that impacts fish health. Trace minerals of import to fish and plants can eventually be depleted. Therefore: Water replacement becomes important.

What if there was a way to make it so the waterchange happened SAFELY, and CONSTANTLY, and EFFORTLESSLY and AFFORDABLY...... What if you eliminated the need to buy dechlorinator???? (Wait a minute, I sell dechlorinator!) Nevermind what I just said!!!!!

Just kidding, you can relieve the owner of the need for dechlor except in emergencies, otherwise, for "the new way to do" water changes, it's not needed *IF YOU DO IT VIA CONSTANT-INFLOW-WATER-REPLACEMENT*

Read on....

When was the last waterchange?
You should be replacing ALL the water in the pond over time, at a rate of about 10% per week, whether you do that all at once, ten per cent per week, or replace thirty percent every three weeks. The larger the "all at once" water change, the worse it is on the fish as far as temperature and other "water mojo" characteristic changes....This is a stressor. Constantly-over-time inflow replacement of water is better by far. CWIC (Constant Water Inflow Change)

If you use CWIC (Constant Water Inflow Change) to replace up to 25% of your water per week, you do NOT need dechlor. When you replace 25% "all at once" you DO need dechlor, unless you're on a well or have a "whole house" water treatment system.

I prefer to run (ceiling-thread, or bury) a black or clear, 1/4 inch irrigation line off a hose bib splitter, with brass adjustable valve at the end, out to the pond to run CONTINUOUSLY.

Items needed:
All items are available at most large hardware stores. Home Depot sells a roll of 100 foot of 1/4" irrigation line and all the appropriate unions, fittings and valves, the total cost to do a whole fish room is about $100. For the normal pond, probably closer to $50. To make measurements simple, try and have ONE feedline and terminating feedline-valve to adjust, instead of several.



  1. Apply the hosebib splitter to the hosebib nearest the pond. This leaves one hosebib for your wife to garden with. Close hers unless she's using it. Attach your 'hosebib-to-1/4-inch-line-adapter', this adapter you just attached is for your fill line and should be left wide open. Put a small sign on the hosebib that says that the main hosebib *and* your irrigation-line-"half" of the hosebib splitter should be left open....
  2. Run 1/4 inch line to the pond.
  3. Attach the 1/4 inch brass valve.
  4. Affix that valve to the waterline somehow so it doesn't plop out and irrigate the floor or lawn.
  5. Bury your line if possible.

If you knick or pop the line you can cut out the leaking-piece and splice in a new piece with the brass unions which are simple.

Do NOT run constant hosebib pressure on the 1/4 irrigation line with the irrigation line valve CLOSED ...or the line MAY eventually expand and burst. I've never seen this but it happened ONE TIME at Pike's Nursery where we've been using this technology on their fish for sale.

To calculate the maximum hose volume. (Optional)

  1. Run the hose "wide open" and fill a five gallon bucket.
  2. Time the process to the second.
  3. If the bucket fills in 45 seconds. That's 5 gallons in 45 seconds, which calculates out to one gallon in nine seconds.
  4. That means, wide open, your hose system can generate 400 gallons per hour, since there are 3,600 seconds in an hour.

To calculate the irrigation system flow volume:

Run the irrigation line into your graduated container and adjust the brass valve down until the flow is appropriate for the chart below.

Make a simple conversion, and run thusly:
Look how simple these calculations are:

If the pond is 3500 gallons = Drop the decimal point back a tenth, to convert to a "maximum non-dechlorinated flow rate" of 350 milliliters per minute and use the following chart:

[Remember there are 10,080 minutes per week.]

For 3,500 Gallons:

Let's do a smaller example:
The pond is 1600 gallons.

CWIC Constant Water Inflow Change It pays to use a couple rubberbands to hold the brass terminating 1/4 inch valve on its setting, lest it open or close more. Also, with a brass fitting immersed in the water, these fittings turn brown, which is okay, chemically and for the fish. If you use a small wrench and tighten the lock nut on the valve, the nut under the adjustment stem, you can stiffen it up, but this also happens over time as the valve ages. As it stiffens, it's harder to adjust up or down, which is a Good Thing from the standpoint of "accidental adjustments" on smaller systems.

Never eyeball the adjustment of the valve on a small system. For example, on a 160 gallon tank, you can do 16 milliliters per minute and that replaces 25% per week with no dechlor needed. Buu-u-u-ut you can see that if the valve gets knocked open a little, you might change MUCH more water too quickly and then get into chlorine issues.....The consolation is that through a 1/4 inch line, even knocked wide open - MASSIVE water flow just isn't really feasible. But in a half whiskey barrel facility, such an accident with chlorinated water would be enough to do some damage.

By running "new" water to the system all the time, you not only replace evaporative losses but you add new buffers, and replace accumulating DOC with healthy fresh water. You eliminate the need for dechlorinator except when you are forced by rare emergency to change a LOT of water at once. And you give the home owner a chance to relax and never drag around a drain pump, and have to stand by while refilling the pond. No matter where the owner is, or what they're doing, they have the satisfaction of know that at the house, they're always doing a water change and it's painless.

QUESTION 1: "Is my pond ready for this?"
It is ready if it can handle rainwater overflow in a gracious manner. If it is not engineered to overflow properly in a rainstorm, it is not engineered for this. CWIC (Constant Water Inflow Change) is a "slow motion" overflow. Ask you installer if the pond and landscape can handle this slow motion overflow.

QUESTION 2: "Won't this dilute my medications?
Yes CWIC (Constant Water Inflow Change) will reduce the salting, if you're doing that. And it will help (at 25% per week) to dispel medications which you MAY or MAY NOT want dispelled. For example, Dimilin must remain resident. You would want to throttle back on the Constant Water Inflow Change unit. Praziquantel is another medicine as well as Supaverm that you may not want to dilute. Formalin, on the other hand is much safer in systems with CONSTANT WATER INFLOW CHANGE.

QUESTION 3: "What about indoor facilities?"
All the math is the same, but instead of the overflow water running into the landscape, you need an overflow bulkhead or standpipe in any tank fed by CWIC and this drain line must flow to safety. Remember the flows are pretty low, on the order of three teaspoons per minute in small 150 gallon systems like you'd have indoors.

QUESTION 4: "Do I still need carbon on systems running with CWIC (Constant Water Inflow Change)?"
Yes and no. In many facilities and ponds, the tannin stain from some trees overhead is furious and will not be defeated by CWIC (Constant Water Inflow Change). In MANY other cases you may notice that the water remains free of the need for carbon while you're running CWIC (Constant Water Inflow Change) in its medium to high flow rates.

QUESTION 5: 'Is CWIC (Constant Water Inflow Change) safe with Chloramine treated water?"
I do not recommend that you run CWIC (Constant Water Inflow Change) at the full 25% per week value in Chloramine treated systems because Chloramine has a longer residence time than regular chlorine which is short. If you use CWIC (Constant Water Inflow Change) in chloramine treated systems, you do so at your own risk (heck, you're doing all of this at your own risk!) but run it at 12.5% maximum. So for 7000 gallons, that would be 350 ml per minute.

QUESTION 6: "Won't this jack up my water bill?"
Uhhh, yeah. But that has alot to do with how big of a pond you've got, and whether you need to change out 25%, 12 %, 6 % or 3% per week.

Special thanks to Pike Family Nurseries (Koi and Pond Supplies, Fish, and Stoneyard) for letting us deploy this system during the testing phase on numerous of their fish holding facilities in the Southeast. Also special thanks to Tommy Hill who installed the systems for anyone who said I could "guinea pig" their pond or tank for a few months, and for putting in most of the CWIC systems in KoiLab which is now 100% CWIC.

"If you're thinking about building your own pond, I salute you and I wish you well. Make sure you lift with your knees, put on lots of sunscreen, find those phone wires and gas lines before you dig, and wear a weight belt. Learn to use a transit to make sure the sides are level. Good luck!
If you're like me, and you want your pond installed FOR you, Get a "Certified Aquascape Contractor."
They're called CAC's and they are ACCOUNTABLE, and they will save you MONEY by saving you TIME (and call backs). Usually, the "credentialed" professional is MORE expensive, but in this case, the opposite is true because you pay for their TIME and because they don't have to refer to a manual or fumble around, they SAVE IT!!!!
CAC's can do what they say they can do, because they are proven installers and they are accountable to the manufacturer and have to back up their work. "Your pond gear is ONLY as good as the installer who puts it in". (A quote from a good friend at Pikes'). I vouch for the CAC's and no one else to give you what I have: The easiest pond ownership experience you can buy, bar none. Find a CAC, "rub the lamp" and tell that genie what you want. Get your pond in, and start enjoying yourself in your own back yard."
- Doc Johnson

(See a note on Algae Control)