Calculator
Alkalinity Dosing Calculator
Alkalinity is the parameter that punishes inattention the hardest. SPS tissue recession at 6 dKH, burnt tips at 12 dKH, neither one recovering fast. This calculator takes a tank volume, your current reading, your target, and a product, and returns the exact mL of liquid stock or grams of dry powder. Every constant traces back to a primary source — Randy Holmes-Farley's original recipe articles, BRS Pharma mixing instructions, Tropic Marin's product label, Red Sea's manual, or Triton's CoreChem documentation.
Alkalinity dosing
594 g sodium bicarbonate baked at 300 °F for 1 hr to Na₂CO₃, dissolved to 1 US gal. Stock ≈ 1,900 meq/L.
Source: reefs.com
How much bicarb that actually is
Sodium Bicarbonate, 100% pure — 5 lb
Burning ~255 g/month, one 5 lb pack covers ~8.9 months · ~$20.
Based on a 75 gal (284 L) mixed reef consuming 1.0 dKH/day, at 3 g of NaHCO₃ per 100 L per dKH. Run your own numbers above — demand scales with tank volume and coral load.
Chemically identical to the alk half of any commercial two-part — 3 g per 100 L raises alkalinity about 1 dKH, and a 5 lb pouch lasts most tanks a year.
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Dosing alk? These are what reefers reach for.
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How this is calculated
Randy Recipe #1 stock = 594 g NaHCO₃ baked → 1 gal solution
≈ 1,900 meq/L
mL_dose = tank_gal × ΔdKH × (3.785 / 1900) / 2.8 dKH-per-meq
For Red Sea Foundation B (1 mL/100 L = 0.034 dKH):
mL_dose = tank_gal × 3.785 × ΔdKH / (100 × 0.034)
For Triton Base 1 (dry):
g_NaHCO₃ = (tank_L / 100) × ΔdKH × 3Randy Recipe #1 is sodium bicarbonate baked at 300 °F for an hour to convert to sodium carbonate (Na₂CO₃). The conversion drives pH up faster than unbaked baking soda (Recipe #2), which is the right choice if your tank pH is already 8.3+ and you don't want it climbing further. Recipe #2 still works but raises pH ~0.1 less per dose at equilibrium.
All-For-Reef is a special case: it's a balanced maintenance product that supplies calcium, alkalinity, and magnesium in the natural ratio of consumption. You can't "raise alk by 1 dKH" with AFR — the math is daily dosing as % of demand. The calculator returns Tropic Marin's recommended starting dose (5 mL / 100 L / day) and the maximum (25 mL / 100 L / day).
Single doses above 2 dKH are flagged as risky. Coral reacts to rate of change, not absolute value. A tank running stable at 6 dKH is healthier than one yo-yoing between 8 and 10 dKH every week — see the alkalinity reference for the full stability discussion.
FAQ
- Why is my dose so small for a 50-gallon tank?
- Randy Recipe #1 stock is ~1,900 meq/L — incredibly concentrated. About 1.4 mL per US gal raises alkalinity by 1 dKH. For a 50-gal raising 1 dKH, that's ~70 mL of stock. Real concentrated stocks make small doses look tiny; that's the design, not an error.
- Recipe #1 versus Recipe #2?
- Recipe #1 (baked) raises pH harder; useful if your tank runs 7.8–8.0 and you want to climb. Recipe #2 (unbaked) keeps pH closer to where it sits; useful if your tank is already 8.3+ and you don't want to chase it higher. The Ca side of the recipes is the same either way.
- Can I mix BRS Pharma soda ash and Randy at the same strength?
- Yes — both target ~1,900 meq/L when mixed at the published ratios. BRS Pharma soda ash is sodium carbonate from the factory (no baking required), so it's faster to mix and slightly more pH-active than Recipe #2.
- Why does Triton give grams, not mL?
- Triton's CoreChem corrections assume you keep dry sodium bicarbonate on a scale. 3 g NaHCO₃ per 100 L = 1 dKH. They prefer this to liquid stocks because there's no degradation in storage and the math is one-step.
Where to buy
DIY two-part is cheapest — baked baking soda (Arm & Hammer) for alk, anhydrous calcium chloride for Ca. Pre-mixed ESV B-Ionic if you want zero prep. Test daily until you know your tank's uptake.
Arm & Hammer Baking Soda — 13.5 lb
Bake at 250°F for 1 hour to convert to soda ash. Cheapest alk source.
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BRS Pharma Sodium Bicarbonate (alkalinity component)
Pre-baked NaHCO₃ for Randy/BRS two-part. Skip the oven step.
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BRS Pharma Calcium Chloride (Ca component)
Anhydrous CaCl₂ for two-part dosing. Use Randy's recipe math.
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ESV B-Ionic Two-Part
Pre-mixed liquid two-part if you don't want to DIY.
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Salifert KH/Alkalinity test kit
The hobbyist standard for alkalinity testing.
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Hanna Marine Alkalinity Checker (HI772)
Digital alkalinity. Quicker than Salifert, similar accuracy.
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<iframe
src="https://reefcalcs.com/embed/alkalinity-dosing/"
width="100%"
height="720"
style="border: 1px solid #1C2D34; border-radius: 8px; max-width: 720px;"
loading="lazy"
title="ReefCalcs Alkalinity Dosing Calculator"
></iframe>Sources & references
- 01Randy Holmes-Farley — A Homemade Two-Part Calcium and Alkalinity Additive System (Recipe #1)https://reefs.com/magazine/aquarium-chemistry-a-homemade-two-part-calcium-and-alkalinity-additive-system/
- 02Reefkeeping — Recipe #2 and #3A updateshttps://reefkeeping.com/issues/2006-02/rhf/index.php
- 03Bulk Reef Supply — BRS Pharma Soda Ash Mixing & Dosinghttps://www.bulkreefsupply.com/content/post/brs-pharma-soda-ash-mixing-and-dosing-instructions
- 04Tropic Marin — All-For-Reef product informationhttps://www.tropic-marin-smartinfo.com/?lang=en
- 05Red Sea — Foundation Complete Manual (Foundation B / KH constants)https://redseafish.com/wp-content/uploads/2020/11/24653_Manual-Foundation-Complete-GB-_v21a-WEB.pdf
- 06Triton — CoreChem product page (Base 1 dosing)https://www.triton.de/en/products/corechem
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