diurnal

I thought I understood this, but when I look at the PH in my tank I realize I can't explain what I'm seeing. What I thought was going on was that the photosynthetic organisms in my tank (corals, algae, ...) were absorbing C02 during the light period, driving up the PH. And it would go down at...

One of the inspirations for getting into reefing was being able to keep weird stuff I couldn't keep in freshwater - especially invertebrates. Turns out a lot of invertebrates are either nocturnal or hiders or both. Anyone have suggestions for day-active invertebrates?