I’ve recently started experimenting with reversal using STS solution. I purchased the chemicals separately, with a recipe provided by my chemist. The challenge is that the recipe requires measuring 0.03 g, but my scale isn’t accurate below 0.05 g.
To improve my approach, I’ve been collecting recipes from different sources, such as The Breeder’s Bible and posts from experienced breeders.
Most agree on a ratio between 3.4:1 and 4:1, but the molarity and molar masses often vary. Some of the older, “original” recipes are also very chemical-intensive, producing 500–1000 ml of solution — far more than a hobbyist needs, since 100 ml or less is usually sufficient.
Because of this, I’ve started considering ways to adjust both the ratios and the molarity, then fine-tune the concentration with water dilutions.
By keeping stock A and stock B separate, I can also extend the shelf life of the solution. Below I’ve compiled some of the initial recipes I found, leading up to Recipe D, which is designed for only 100 ml of solution at a 3.4:1 ratio.
Recipe A — 0.03 g AgNO₃ + 0.18 g Na₂S₂O₃·5H₂O in 300 mL (final)
AgNO₃ moles = 0.03 / 169.87 = 0.0001766 mol
Na₂S₂O₃·5H₂O moles = 0.18 / 248.18 = 0.0007253 mol
Molar ratio (S₂O₃²⁻ : Ag⁺) ≈ 0.0007253 : 0.0001766 ≈ 4.11 : 1
Final concentrations:
[Ag⁺] ≈ 5.89×10⁻⁴ M
[S₂O₃²⁻] ≈ 2.42×10⁻³ M
Recipe B — make stocks: 0.5 g AgNO₃ in 500 mL and 2.5 g Na₂S₂O₃·5H₂O in 500 mL, then dilute 1:9 (i.e., 1 part stock + 9 parts water → 10× dilution)
Stock concentrations (in 0.500 L):
[Ag⁺]stock = (0.5 / 169.87) / 0.5 = 0.0058875 M
[S₂O₃²⁻]stock = (2.5 / 248.18) / 0.5 = 0.020139 M
After 1:9 dilution (÷10):
[Ag⁺] ≈ 5.89×10⁻⁴ M
[S₂O₃²⁻] ≈ 2.01×10⁻³ M
Molar ratio ≈ 3.42 : 1
Recipe C
AgNO₃: 0.1 g
Na₂S₂O₃·5H₂O: 0.584 g
Dissolved in 300 mL of distilled water, then diluted 1:2.33 with water
Since 0.584 g is also hard to weigh precisely, I considered the effect of variability in the Na₂S₂O₃·5H₂O chemical, while water is easy to adjust after, maintaining more achievable numbers. The ratio is now in the range of 3.4 and 4:1 so between recipe A and B.
Recipe D
100 mL stock:
Stock A: 0.05 g AgNO₃ in 100 mL water
Stock B: 0.25 g Na₂S₂O₃·5H₂O in 100 mL water
Example solution:
Mix 50 mL Stock A + 50 mL Stock B → 100 mL mixture
Add 150 mL water → final volume 250 mL
[Ag⁺] ≈ 5.89×10⁻⁴ M,
ratio ≈ 3.43:1 ( like recipe 2)
Ultimately, ratio, molarity, concentration, and spray application are all connected. Higher concentrations with higher molarity may require fewer sprays (perhaps only one or two), while lower molarity could mean more frequent applications. Outside of the math — formulas, molar masses, and so on — the practical side of application still feels confusing to me. I’d really appreciate if anyone could share their tried-and-tested recipes and spraying protocols.
