That's fine. And some people use it OK to keep very fine looking aquaria.
But you can do that easier and cheaper and with less concern using a product which you know what it adds and how much it adds, and not support a company that makes misleading claims.
Here are some examples from their advertising copy which simply are not true:
SEA-LAB No.28 Replenisher Block is an automatic replenisher block. It restores and maintains the concentration of calcium, strontium and all trace elements at the same levels found in the sea, automatically.Sea Lab No. 28 Replenisher Block always works, and cannot be overdosed. This is not a slow-dissolve or time-release product. It dissolves only to replace depleted elements.
Naturally occurring buffer compounds maintain ideal saltwater chemistry. Eliminates major water quality problems and limits phosphate, ammonia, and heavy metals. Also buffers pH and provides a constant supply of vital calcium, as well as all other essential trace elements and microelements. Dissolves slowly for gradual change - no possibility of harmful overdose.
Calcium and strontium are well-recognized nutrients, but trace elements are not as well understood.
Formula #28 is the first formula available to hobbyists and the professionals that create and maintain this balance. As elements are depleted from solution, Formula #28 delivers exact equivalent amounts to replace them.
And for laughs, one advertisement says
"This is not a slow-dissolve or time-release product."
and a second one says
"Dissolves slowly for gradual change"
