Wait a sec..you have or had coraline algae growing in a freshwater tank?
If so...what was the ph? I'd love to experiment with a 20 long I have, and see if I could do a "false marine" tank with small species of rift lake ciclids!
Check your tap water before you invest in expensive coral based marine sand. If you have municiple water, almost certainly they add corrosion control chemicals and your water will be higher than pH of 7.0 and at least some significant hardness. The rift lake cichlids available today are from several generations of breeding stock raised in average US water conditions. As long as the water isn't crazy soft and pH lower than 7.0, they will thrive and breed in anyones tap water without addition of calcerous substrate.
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