Hi barb,
:gw Given the possibilities, (we might say a gram measure when we mean teaspoon, etc.) some variation is to be expected. What is the actual weight and how to calculate grams from teaspoon measurements of Fe Gluconate is all prone to error. They should be close, but hardly exact. I used my favorite two calculators to answer your question.
24.0 tsp Fe Gluconate into 500.0 mL container, dose of 1.0 mL into a 15.0 gal tank = 0.26ppm
Seachem Iron
dose is 1.0 mL
into a 15.0 gal tank and:
Fe = 0.26ppm
http://www.fishfriend.com/fertfriend.html
Your dose of 13.5 tsp Fe Gluconate into your
500.0 mL container, and a dose of 1.0 mL
into a 15.0 gal tank gives:
Fe = 0.145ppm
http://calc.petalphile.com/
24.0 g Fe Gluconate into
250.0 mL container,
dose is 1.0 mL
into a 15.0 gal tank and:
Fe = 0.211ppm
http://calc.petalphile.com/
8.0 tsp (16tsp) Fe Gluconate into
250.0 mL (500mL) container,
dose is 1.0 mL
into a 15.0 gal tank and:
Fe = 0.171ppm
http://calc.petalphile.com
15gal. = 38 Liters