PondTools

Seasonal care

Spring pond cleanout: step by step, and when to restart pump and feeding

Spring pond cleanout: step by step, and when to restart pump and feeding

Do the cleanout early, while the pond is still below about 55 degrees Fahrenheit. Pump the cleanest water into a shaded, aerated holding tank first, catch the fish only when a few inches of water are left, rinse from the top of the system down, and refill with a dechlorinator that also handles chloramine. Return the fish when the bucket and the pond are within a few degrees of each other. You can run the pump as soon as the skimmer has water. Hold off on feeding until the pond stays at 50 degrees or above, which is the threshold Aquascape and the Minnesota Water Garden Society both give. If the pond still looks the way it did last June, a no-drain tidy-up with a 10 to 20 percent water change is enough.

What the authoritative sources say

No extension service publishes a pond cleanout procedure, so the fish-handling numbers come from veterinary and aquaculture references written for other settings. The Merck Veterinary Manual says "Sudden changes in temperature, of even just a few degrees, can result in compromise of immunity," and gives "1°F, or even 1°C, per hour as a maximum change" as a general rule. It reports "adverse effects occurring at chlorine concentrations as low as 0.02 mg/L and mortality at 0.04 mg/L," and warns that when chloramine is treated with sodium thiosulfate, "ammonia is released into the system," so it recommends a dechlorinator that also binds the ammonia.

The University of Florida's On-Farm Transport of Ornamental Fish (FA119, 2004), written for fish farms, treats a gap of more than 5.5 degrees Celsius (10 degrees Fahrenheit) as one that needs acclimation, and says that above 10 degrees Celsius "acclimation should proceed slowly over a period of two or more hours." Tampa Bay Water, a utility, says monochloramine "may take weeks to dissipate," so letting tap water stand overnight does not make it safe.

For timing, bacteria and feeding, the only published rules are Aquascape's rules for its own program. Its spring cleaning guide says to clean "ideally before the water temperature in the pond creeps above 55º F," because a later cleanout upsets the bacteria and brings "another period of algae blooms." Its spring koi page says to avoid feeding "until the pond water consistently reaches 50 degrees Fahrenheit," and its March checklist recommends cold-water bacteria "When water temperatures are between 32°F and 50°F."

Spring temperature thresholds, by source. Each is that source's own rule.
DecisionWater temperatureSource
Do the cleanoutBefore the pond goes above 55°FAquascape
Cold-water bacteria32°F to 50°FAquascape
Start feeding, sparinglyConsistently 50°FAquascape
Resume feedingRemains above 50°FMinnesota Water Garden Society
Start feedingAbove 55°FGrass Roots Pond & Garden
Switch to higher-protein foodStable above 60°FAquascape
Holding tank against pondWithin 5 degreesAquascape contractor article
Maximum rate of change1°F per hourMerck Veterinary Manual

What contractors and the retailers do

The full-drain sequence is much the same everywhere. The Pond Guy's spring startup page says to drain "until there is about one foot of water left," hold fish in "a clean kiddie pool, holding tank or even a Rubbermaid Tub" with an aeration kit, give them "about 20 minutes to adjust," and wait "24 hours" before feeding. Aquascape's consumer guide says not to keep fish in the pool "for more than several hours." Its contractor system (April 2026) works "BioFalls → stream → pond → skimmer," pumps the cleanest water into the holding tanks before debris is stirred up, and catches fish "When water levels drop to just a few inches."

After several of a customer's koi died following a cleanout, Gary Wittstock changed his process, as Aquascape tells it in How to Avoid Fish Loss During Pond Cleanouts. The customer stops feeding "one week in advance," the crew keeps "more of the existing pond water," moves fish in a container instead of a net, adds a submersible filter to the aerated holding tank, and keeps tank and pond "within five degrees of each other." Aquascape's cleanout services article returns fish once the pond "is approximately 1/3 filled" and floats them "for 10-15 minutes."

Practitioners disagree on several points. Ponds By George in Southampton, Pennsylvania nets fish "immediately after we begin the draining process," while Doug Hurth of Hurth Waterscapes in Wisconsin says "Don't even try to catch the fish until you have most of the water out." Hurth says of the tank, "The bigger the better," and Pond Doctor in Southern California uses a "hospital tank (500 Gallon Pool)." Aquascape says several hours at most, but Aquatic Edge near Pittsburgh says fish "may rest safely overnight in our large holding tanks." Grass Roots Pond & Garden waits for 55 degrees to feed, five degrees later than Aquascape.

Skipping the drain is a legitimate choice, and it costs less. The Pond Guy's quick cleanup is to "Drain 10 to 20 percent of the water," vacuum the bottom, rinse the filter media and add cold-water bacteria. Aquatic Edge prices a full drain from $720 and a no-drain "Basic Spring Start-up" at $360. Aquascape's test is visual: a sludge layer and dark water mean a full cleanout, and its contractor article says "If the pond looks the same in March as it did last June, it's probably okay to take a pass." For what a professional cleanout costs and how long a crew takes, see pond maintenance contract pricing.

Where the tiers differ

The biggest gap is acclimation time. The industry's 10 to 20 minute float is far shorter than Merck's one degree per hour, which would take five hours to close a five degree gap. A float is enough when the holding water came out of the same pond an hour or two earlier, so the gap starts small. It is not enough when the tank sat in the sun, or when the pond was refilled with 50 degree well water and the fish are in 58 degree water. The holding tank's job is to keep that gap from opening.

The second gap is the dechlorinator. Merck and Tampa Bay Water treat chloramine as a separate problem from chlorine, while the Pond Guy's startup page says only that its conditioner will "remove any chlorine." Look for chloramine and ammonia on the label, and ask the water utility which disinfectant it uses.

No authoritative source gives a holding-tank size for a cleanout; the kiddie pool and the 500 gallon pool are practitioner choices. A 6 foot kiddie pool with a foot of water holds about 210 gallons. Even a 300 gallon tank holds only 6 percent of the water in a 5,000 gallon pond, so the same fish sit about 17 times as crowded. That is why every source insists on aeration, shade, a net and a short stay, and why fish that have not been fed for a few days are easier to hold.

What to do

  1. Put a thermometer in the pond in March. Plan the cleanout while the pond reads below 55 degrees, on a day when the fish look healthy. Stop feeding a week ahead.
  2. Decide drain or no drain. Do a full drain for a sludge layer, dark water or a repair. Otherwise change 10 to 20 percent of the water, vacuum the bottom and rinse the filter pads.
  3. Set the holding tank in shade, aerate it, and fill it first with the clearest water from the top of the pond. Cover it with a net.
  4. Catch fish when only a few inches remain, and move them in a bucket of water. Check the tank temperature against the pond every hour.
  5. Clean from the top down: falls, stream, pond, skimmer. Rinse until the water at the pump runs clear, and leave some algae on the rocks rather than scrubbing them bare.
  6. Refill, and dose a dechlorinator that lists chloramine for the full volume of new water. Aquascape Pond Detoxifier is labeled "One pump treats up to 100 gallons of water" (Webb's), and a 1 gallon jug treats up to 80,000 gallons (The Pond Shop), which is 1.6 ounces per 1,000 gallons. Never put fish into untreated city water.
  7. Restart the pump once the water covers the skimmer intake, and add the cold-water or starter bacteria the label calls for.
  8. Float the fish in buckets of holding water for about 15 minutes, then splash in pond water a little at a time. If the gap is more than 5 degrees, take longer. Do not tip fish from the holding tank into colder new water.
  9. Feed nothing for at least a day, then feed lightly only once the pond holds at 50 degrees or above.
Aquascape Pond Detoxifier for a full refill, at the label rates above (1.6 ounces or ten pumps per 1,000 gallons)
Pond volumeOuncesPumpsNo-drain change, 10 to 20 percent
1,000 gallons1.610100 to 200 gallons
3,000 gallons4.830300 to 600 gallons
5,000 gallons850500 to 1,000 gallons
10,000 gallons161001,000 to 2,000 gallons

The PondTools volume and water-change calculators

Every dose above depends on knowing the gallons. The PondTools volume calculator (also standalone) takes length, width and average depth in feet plus a shape, and shows how far the simple box formula overstates a real pond. The PondTools water-change calculator (also standalone) takes the pond volume, the current reading (nitrate, for example), the target and what the tap water reads, and returns the gallons to replace, with the effect of a series of smaller changes alongside. It will tell you whether a 10 to 20 percent no-drain change gets you there or the pond needs the full drain.

Sources