Crushed Oyster shell is inexpensive, aragonite can be pricey, but both do the same thing. The acids that lower pH leach calcium from each.
In the states, beside mixed in with substrate, I used fine grain aragonite as media in a fluidized bed reactor. After a few months I would add a litte more to keep pace with the amount that had been used up by metabolism (acids).
The reactor held about 5lbs of aragonite and stood about 4ft high, 8" in diameter.
After adding new aragonite, the water in the tanks would sometimes get a bit milky (seen in the last pic), the reactor covered a line of 4 or 5 tanks, on the barrel sump, in total equaling about 300-400 gallons.
In the states, beside mixed in with substrate, I used fine grain aragonite as media in a fluidized bed reactor. After a few months I would add a litte more to keep pace with the amount that had been used up by metabolism (acids).
The reactor held about 5lbs of aragonite and stood about 4ft high, 8" in diameter.
After adding new aragonite, the water in the tanks would sometimes get a bit milky (seen in the last pic), the reactor covered a line of 4 or 5 tanks, on the barrel sump, in total equaling about 300-400 gallons.