Safer partial drains for balanced water quality. Enter tank size, current levels, and desired target. See how much to drain and refill instantly now.
This calculator uses a simple dilution and mixing model for a single drain-and-refill. When you drain a fraction f and refill with source water, the final concentration becomes:
The drain volume equals f · V. Refill volume matches the drain volume. If the computed fraction is outside 0–1, the tool limits it for safety.
| Scenario | Total volume (L) | Current | Source | Target | Drain % | Drain volume (L) |
|---|---|---|---|---|---|---|
| Koi pond nitrate reduction | 5000 | 80 | 0 | 40 | 50.00% | 2500 |
| Small tank refresh | 400 | 30 | 2 | 15 | 53.57% | 214.29 |
| Salinity step-down | 1200 | 3500 | 500 | 2000 | 48.00% | 576 |
A partial drain lowers an unwanted level by replacing a portion of water with cleaner source water. This is safer than a full change because temperature, pH, and beneficial biofilms shift less. The result depends on starting concentration, source concentration, and the target you choose. When source water contains some of the same compound, the achievable reduction is limited.
Volume is the multiplier for every decision, so verify it using dimensions, a flow meter, or a fill‑time test. Use a reliable test kit for the current level and repeat the reading to reduce sampling error. Measure the source level from the hose, well, or storage tank because it can vary seasonally. If you treat refill water, keep your conditioner dose aligned with refill volume, not total volume.
The drain fraction is a percentage of the system volume that must be removed and then refilled. For example, moving from 80 to 40 with a source level of 0 requires a 50% drain. If the computed fraction exceeds 100%, a single drain cannot reach the target; plan multiple stages. If it falls below 0%, your target is already met or the target is higher than current.
Pump rate turns drain volume into minutes, helping you schedule work and avoid running equipment dry. Water cost per 1000 liters provides a budget estimate for maintenance. Conditioner dose per 1000 liters supports consistent dechlorination or buffering with any unit you prefer. Always add chemicals after refilling and mixing, unless the product label specifies otherwise.
Drain slowly to protect liners and avoid stirring deep sediments in ponds and tanks. Refill in stages and circulate water to prevent localized stress on fish and plants. Retest after mixing to confirm the final level, then adjust with a smaller follow‑up drain if needed. Keep a log of readings, drain percentages, and refill sources to improve future accuracy.
It is the level of the same parameter in your refill water. If your hose, well, or stored water already contains the compound, your final level cannot drop below that source value after refilling.
Yes. The math works for any measurable concentration where mixing is linear. Enter values in the same unit each time, such as ppm, mg/L, or EC points.
Your target is too low for a single drain given the current and source values. Reduce the target gap, improve source water quality, or perform multiple smaller drains with mixing and retesting.
For large systems, staged drains are gentler. Drain part, refill, circulate to mix, then retest. Repeat until you reach the target while keeping temperature and pH changes controlled.
Time is based only on the pump rate you enter and assumes steady flow. Real times vary with hose restrictions, head height, filters, and pump performance. Use it for planning, not certification.
Dose the conditioner for the amount of new water you add, because that is the portion needing treatment. If the product label recommends full‑volume dosing, follow the label and treat as directed.
Important Note: All the Calculators listed in this site are for educational purpose only and we do not guarentee the accuracy of results. Please do consult with other sources as well.