How to use this Master Blend tool
Set your options in the calculator above, read the result, then verify with a calibrated meter when the decision matters. Bookmark this page for reservoir day — consistent units beat copying numbers from charts that never name their scale or bottle rate.
Formula reference
Grams = volume (gal) × rate (g/gal) × strength
Why people still run MasterBlend
MasterBlend 4-18-38 plus calcium nitrate and magnesium sulfate is a long-running dry-salt recipe for hobby hydroponics. You buy three bags, weigh grams, and avoid bottle markups — but you also own the mixing mistakes if you rush.
This calculator scales common g/gal starting points to your tank. It does not replace an EC meter. Different water sources and crop stages need different final strength.
Mixing order that avoids sludge
Fill with water first. Dissolve MasterBlend thoroughly. Add Epsom salt next. Add calcium nitrate last, into a swirling tank. Never dump dry MasterBlend and calcium nitrate into the same dry scoop or concentrated jug — calcium phosphate can precipitate and leave plants short.
After mixing, read EC, then adjust pH. Leafy greens often land lower than fruiting tomatoes; use the strength slider rather than inventing a fourth bag on day one.
Presets are starting points
The leafy preset (about 2.4 / 2.4 / 1.2 g per gallon) is a common beginner chart, not a law of physics. Fruiting crops often run heavier once plants are established. Half strength is useful for seedlings and sensitive varieties.
If your tap water is already hard, calcium may run high before you add CalNit — measure source EC and watch for tip burn. RO or soft water usually needs the full CalNit portion.
Frequently asked questions
Is MasterBlend the same as a bottled A/B nutrient?
No. It is a dry three-part salt approach. Bottled A/B lines are convenience concentrates with different ratios. Do not mix charts across brands.
Can I premix a concentrated MasterBlend stock?
Keep calcium nitrate separate from the MasterBlend/Epsom side in stock jars. Combine only in the dilute reservoir.
What EC should I hit?
Many leafy runs sit roughly 1.0–1.6 mS/cm; fruiting crops often run higher later. Always verify with a meter after mixing.
Related calculators
- Nutrient Mixing Calculator — Calculate exact nutrient amounts for your reservoir based on volume and concentration ratios.
- EC to PPM Converter (500 vs 700) — Convert between Electrical Conductivity (EC) and PPM across 500, 640, and 700 TDS scales.
- pH Adjustment Calculator (Up/Down) — Estimate how much pH Up or pH Down solution is needed to reach your target pH.
Keep learning
Pair this calculator with our pH & EC guide, crop targets in plant guides, and meter picks in product reviews.