There are 3 basic Sustain products, but the "Sustain® 3-Inch Blue Chlorinating Tablets" are slow-release cal hypo (calcium hypochlorite) should be OK to use. The "Sustain® ¾-Inch Shield Energizer Tablets" are also cal hypo -- probably fast release, and are also probably OK. Do *NOT* use the "Sustain® Summer Shield Chlorine Extender".

Just make SURE that there are no trichlor tabs in the skimmer at the same time as the Sustain tabs; very bad things will happen if you mess this bit up!