Yes, if you need it. I used Equilibrium for over two years in three tanks, but I discontinued and am now just using the Flourish Tabs plus a limited dose of Flourish Comprehensive Supplement. In my situation, this has been better. I'll explain.
Flourish Comprehensive Supplement does contain the "hard" minerals, calcium and magnesium, and everything else. For most water that has a GH of around 4 or higher, the calcium and magnesium will be present and the minimal amount in FCS adequate. [I am thinking low-tech or natural here, not high-tech with intense light and diffused CO2.] My source water is basically zero GH, so Flourish Comprehensive alone is not sufficient in these hard minerals. I used it to raise the GH in the tank from zero to 5 or 6 dGH. But there is a down side to this, and that is that being in the water column, it impacts fish and may contribute to algae, depending. If you are using it with moderately hard water fish, this is less of a problem, depending upon your source water GH. There may be no need for Equilibrium.
When I stopped using it (which was in order to isolate a specific issue in one tank and water additives were discontinued), rather than starting again I decided to use Flourish Tabs. This has proven effective; the swords which previously showed severe calcium deficiency are thriving, and the tabs do not leech minerals into the water so the fish and algae issues are no more. I've been using the tabs alone for almost two years. Instead of replacing them every 3-4 months, I replace them every 6-8 weeks; I add them when I clean the canisters so it is easy to remember.
One side issue was cloudy water; Seachem says it will dissipate in a couple hours, but this is not the case; it took overnight to completely clear, and not always then. It also takes some effort dissolving the Equilibrium in water before pouring it into the tank (it is a powder, not a liquid product). Seachem now make a liquid GH additive in their newer AquaVitro line, though that is very expensive if you have large and/or multiple tanks.
Byron.
