Scott!Even a tiny amount of copper can be a problem to inverts and octopuses are perhaps the most sensitive. The general consensus is to avoid even tanks that have been exposed to copper medications if they are sealed with silicone (copper retention in acrylic is uncertain).
Yes they can get through the weir (or as I call them castle turrets
) You should to do something to inhibit access, particularly for small animals. Placing something inside the weir is one of the easiest solutions. You want something that feels rough and I have had very good success with very course sponge. I do suggest (and have had tank overflow before doing this) placing something around the bulkhead to ensure the sponge does not block water-flow as it collects debris and compresses. For my problem tank (bottom bulkhead, my others all have side exits and are less of a problem) I cut strips long ways along the sides of a plastic bottle (leaving the top and bottom of the bottle unmodified) to fit over the bulkhead and under the sponge to keep it from settling into the bulkhead opening. For side/back exits, there is a pre-made guard (both screw in and slip in depending upon the inside of your bulkhead, link for example, not a vendor recommendation but the pricing is about what I remember). I always have these fittings (before these were available I used a similarly shaped piece that you find at the end of a cascade filter) on my other bulkheads as they also prevent snails and hermits from entering the overflow lines. Except for small animals (very young or dwarfs), they have worked well by themselves (again, for side exit only and have had little ones get to the sump without a sponge). You can help dissuade curiosity by ensuring arms will meet a rough surface when they explore and by adding a light over the weir but it is hard to localize the light and anything rough will collect debris.
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). Not only is splashing going to happen but just the evaporation will rust your plug prongs. Please consider a ground fault connection with it being that close to the water. If you can't add on at the wall plug (there are plug-in models but they stick out a lot) seriously consider replacing the circuit breaker.
