Aerate the bottom before next summer, then retest before spending more.
That shuts off what's feeding the bloom. Start this week with three free steps; spend first on the one fix aimed at your cause, and let the six-month retest decide the rest. Every cost says what it buys.
This week
- Keep pets out of the water and away from scumYouFreeProtects your dogs now: microcystin is present.Print a warning sign →
- Stop copper treatmentsYouFree, and it ends that billCopper sinks dead algae into the muck, which feeds the next bloom.Send this to your pond company →
- No fertilizer within 10 ft of the water; bag clippingsYou or your landscaperFreeCuts the runoff that adds to the problem after storms.Send this to your landscaper →
Before next summer
- Bottom aeration: one diffuser over the thickest muck (map ①)A proDo thisEst. $2,500–4,000 installed, ~$150/yr powerCuts summer algae about 45% (35–55), enough to reach the healthy range: an oxygenated bottom stops releasing phosphorus. The equipment runs 10+ years.Connect with installers →
- Alum treatment, dosed to your muckA proOnly if the retest says soEst. $1,000–2,000, one applicationTakes the total cut to about 68% by binding what aeration can't reach. You only buy it if the 6-month retest shows the bottom still releasing.Connect with applicators →
This year
- Clean out the storm-drain inlet (map ②)Your HOA or boardDo thisEst. $300–800Stops leaves and silt from rebuilding the muck you're paying to fix.Connect with a contractor →
- A 10-ft native-plant buffer along the lawns (map ③)Your HOA or boardOptionalEst. $1,000–3,000With the inlet cleanout, cuts summer algae about 12%. Filters storm runoff for years with little upkeep.Get the planting list →
Prove it worked
- Retest in 6 monthsUsIncluded with $299/yrShows whether the aeration worked, and whether you need the alum at all.Schedule your retest →
- Monthly satellite watchUsIncluded with $299/yrAn email if it turns greener than its normal, so you act early.Turn on alerts →
- Committed this year
- $2,800–4,800 aeration + inlet cleanout, plus ~$150/yr power
- Only if the retest says so
- +$1,000–2,000 alum treatment
- Optional
- +$1,000–3,000 native-plant buffer
You start with the one fix aimed at your cause, then let the retest decide the rest. Example figures; your report uses quotes from vendors near you.
- Copper algaecide: it clears the water for a few weeks and makes the cause worse.
- Dyes or bacteria products alone: they don't touch the phosphorus in the bottom.
What each fix costs, and how much it cuts your algae.
Our scientists ran 16 fixes and 38 combinations through our proprietary pond model, developed and field-tested in our own research and calibrated to your lab results, satellite history and weather. "Summer algae" is the average chlorophyll from June to September: yours is 28 µg/L today, and the healthy range for a Southeast U.S. stormwater pond is under 20.
Worth paying for · the shortlist, best value first
See all 38 combinations →| Rank | Option | Up front | 5-year cost | Cuts summer algae by | Healthy range? | Lasts | |
|---|---|---|---|---|---|---|---|
| 1 | Bottom aerationBest valueone diffuser + compressor | $2.5–4k | $3.3–4.8k | 45% (35–55) | Yes | 10+ yrs, ~$150/yr power | |
| 2 | Aeration + alumBiggest cut for the moneyalum only if the retest says so | $3.5–6k | $4.5–7k | 68% (58–78) | Yes | Aeration 10+ yrs; alum 3–5 | |
| 3 | Aeration + lanthanum claycosts more than alum, lasts longer | $4–7k | $5–8.5k | 72% (62–82) | Yes | Aeration 10+ yrs; clay 5+ | |
| 4 | Alum alonebinds the bottom's phosphorus | $1–2k | $2–4k | 30% (15–40) | Borderline | 3–5 yrs, then re-treat | |
| 5 | Runoff stepsinlet cleanout + native buffer | $1.3–3.8k | $1.5–4k | 12% (5–20) | No | Years, light upkeep | |
| Keep treating with copperwhat you do today | $0 | ≈ $3k | 0% lasting | No | Clears it for a few weeks | ||
Ruled out for this pond, and why
- Dredging removes the muck, but $30–60k and permits, even at this size
- Surface fountain mixes the top; barely reaches the bottom (≈10%)
- Pond dye shades the water; no lasting cut
- Bacteria products no proven effect on bottom phosphorus
- Barley straw weak, inconsistent results
- Ultrasonic units no lasting cut in field trials
- Grass carp eat plants, not algae
- Copper or peroxide algaecides clear it for weeks, then feed the next bloom
Every combination
15 of the 38: expected summer algae (µg/L) and up-front cost. Green = inside the healthy range.
Today: 28 µg/L · healthy range: under 20 · ★ best value · ● biggest cut for the money
Cost vs. result
Every modeled combination (grey). The line joins the best-value ones: anything below it costs more for a smaller cut.
Our recommendation: start with bottom aeration. It's the best value and should bring summer algae into the healthy range on its own. Retest in six months; add alum only if the bottom is still releasing. That path is rows 1 and 2, paid for in two steps.
Example figures for a 1.2-acre pond. Ranges show model uncertainty; your report uses your pond's model and quotes from vendors near you.
The pond bottom is feeding a blue-green bloom.
Years of settled leaves, clippings and algae have built a phosphorus-rich muck. In hot, calm weeks the bottom water runs out of oxygen and the muck releases that phosphorus, along with ammonium. Blue-greens (cyanobacteria) take it up fastest, so they've taken over. Runoff adds to it after storms, but it isn't the main cause.
Confidence: high. The satellite record, the weather and the lab all point the same way. A bottom-oxygen reading next summer would confirm the timing.
- Hot, calm weeks8 days at 95 °F or more; light wind before you sampled
- The bottom loses oxygen86 °F water and 14% muck use it up
- The muck releases phosphorus and ammoniumSediment phosphorus 2× the range; ammonium high, nitrate low
- Blue-greens winNitrogen-to-phosphorus 15 : 1 favors them; pH 8.9
- Green water, toxin presentChlorophyll 28 µg/L; microcystin below the swim advisory
Satellite from your free read
Greener than its own normal every summer since 2024, and greener each year. A pattern, not one storm.
Weather from your free read
- Rain, 30 days before sampling
- 9.4 in · 1.6× normal
- Days at 95 °F or more
- 8
- Wind, the week you sampled
- Calm, under 5 mph
Heat and still air let the bottom water lose its oxygen.
Lab your kit
10 of 17 results outside the range for a Southeast U.S. stormwater pond
The bottom holds twice the usual phosphorus. Ammonium is high while nitrate is low: the nitrogen is coming up from the muck, not off the lawns.
- Release from the pond bottomMain driverPhosphorus-rich muck, ammonium high, greener every summer
- Storm runoffContributesRain 1.6× normal, but turbidity in range
- Lawn fertilizerMinor nowNitrate is low
| Test | Result | Flag | Range: Southeast U.S. stormwater pond |
|---|---|---|---|
| Water | |||
| Total phosphorus | 72 µg/L | H | < 50 µg/L |
| Dissolved phosphate | 18 µg/L | H | < 10 µg/L |
| Total nitrogen | 1.1 mg/L | < 1.3 mg/L | |
| Ammonium | 0.21 mg/L | H | < 0.10 mg/L |
| Nitrate + nitrite | 0.03 mg/L | < 0.30 mg/L | |
| Chlorophyll-a | 28 µg/L | H | < 20 µg/L |
| Turbidity | 8 NTU | < 10 NTU | |
| pH (afternoon) | 8.9 | H | 6.5–8.5 |
| Conductivity | 310 µS/cm | < 1,000 (fresh) | |
| Alkalinity | 64 mg/L | 20–150 mg/L | |
| Test | Result | Flag | Range: Southeast U.S. stormwater pond |
|---|---|---|---|
| Bottom | |||
| Sediment phosphorus | 1,450 mg/kg | H | < 700 mg/kg |
| Sediment nitrogen | 5,400 mg/kg | < 6,000 mg/kg | |
| Organic matter (muck) | 14% | H | < 10% |
| Algae | |||
| Dominant algae | Microcystis | H | Mixed, no blue-green |
| Blue-green cells | 38,000/mL | H | < 20,000/mL |
| At the bank | |||
| Clarity (Secchi) | 0.7 m | L | > 1.0 m |
| Water temperature | 86 °F | 78–90 °F (Aug) | |
| Toxins* | |||
| Microcystin* | 1.8 µg/L | Det. | < 8 (EPA swim advisory) |
| Cylindrospermopsin* | Not detected | < 15 (EPA swim advisory) | |
| Anatoxin-a* | Not detected | Not detected | |
H above the rangeL below the rangeDet. detected, below the advisoryRanges are for healthy ponds of your type in your region.
How this report was made. Your results run through WaterDx's proprietary pond models, developed and field-tested over years of our scientists' published research, not a generic AI. Software handles the routine work; a scientist reviews and signs off on every report before it reaches you.
* Toxin add-on only (+$89, fresh water).