Water Treatment Blocks
Some aquarium water treatments are available to buy in an easily administered block. No mess or fuss, just drop the block into your aquarium.
The binders that make up these products usually consists of calcium compounds. As a result you may notice an increase in pH and hardness after use. This buffering action will gradually be neutralized after the block has dissolved. This is also true of aquarium feeder blocks.
The blocks will generally dissolve faster in acid water but will still take sometime. This allows the active ingredients to enter the fish's environment gradually.
Aquarium Water Reading
Aquarium Water Guide