BGA (blue green algae), also known as Cyanophyta,  which is extensive and highly visible blooms with the appearance of blue-green colour and is toxic.
 
The tabs will decompose the BGA and then the BGA will be separated from gravel/soil/plants and kept to be decomposed w/ 3days.

Dosing
                                                   Max.
tank(cm)/litres(L)      allowable dose
30x18x20cm(11L)            5Tabs
40x23x25cm(23L)           10Tabs
45x28x30cm(38L)           20Tabs
50x30x30cm(45L)           25Tabs
60x30x36cm(65L)           30Tabs
60x40x40cm(96L)           50Tabs