Here are a few of my ideas:
There are lots of workshop suggestions for DIY stuff (calc reactors, skimmers).
What if we had a meeting announcement that had a paypal link for the supplies?
Say we are doing one for protein skimmers. You click the link and pay your $50 or whatever. Based on the number of paying students, some of the subject matter experts from the club get together and buy the supplies in bulk and have the stuff all precut.
We all show up for the meeting and non-students can watch and listen while paying students build their skimmer under the watchful eye of our instructor members.
Buying the components bulk saves on shipping and wasted scraps. If the price is set right, the instructor members could possibly be paid a token of appreciation from the leftovers. Or any leftover money could be used for building some extra units for door prizes or raffle.
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On a totally different note, but equally interactive, we could all bring in sand samples from our tanks or refugium. We could bring in some borrowed microscopes with camera attachments. Then we could look at how lively different members sand in and the pictures could be put in a slideshow. This could also be displayed live with a video camera hooked to a microscope. A computer projector would be great for this.
If this were combined with a talk on refugiums or deep sand beds, I bet it would be a hit.
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How about a meeting where members make their own artificial live rock from aragocrete like here:
http://www.garf.org/class.html
This could be combined with a talk about why you might want to do this.
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A talk on tips and trick to avoid disaster might be nice. For instance what safeguards can be put in place to keep from flooding your carpet, or worse, your neighbors below you. If a large snail decides to crawl into the external overflow box and blocks the siphon tube to the sump, what will happen. If the power goes out, is anything bad going to happen immediately? How much time do you have, and what key equipment might be good to have on a battery backup system? Just a few ideas along that line.
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What about a discussion on the types of tasks that are easy to automate? Dosing, feeding, cleaning…