How many gallons is the tank they are in? It is possibly a "space" related issue, they might feel crowded if the tank is too small.

Model numbers are usually coded with the year of introduction to the market. Serial numbers are coded with the date of manufacture, typically either year & month or year & week. Each manufacturer uses a different coding syntax. Some are fairly easy to figure out, others require a decoding chart. Some manufacturer coding methods are outlined here: How old is my appliance?

You've done really well with this steal of a deal!

What a fun thread. I love the playing card idea. You can get clear labels in many sizes to print on your computer then stick it onto a vintage playing card or what ever and the design will show through. I have some clear labels here at the office, elephantear. I'll take some home tonite and see if they stick to concrete. Something else that occurs to me is you can probably print on masking tape if you buy the wider one and really stick it down good on a piece of transparency film or something with some bulk that you can remove the tape from after. I've done similar with scrapbooking - that is printed on a little piece of paper that I've already cut out by sticking it onto something 8.5 x 11. Here is a scan of transparancy film with masking tape and printing that I just quickly did this in word as an example. I kind of like the rustic look of the masking tape. In order to get the space right you would type up a full page of what you want in Word and print it on plain paper to check if it is spaced right for your masking tape "layout" then adjust. The transparency film with tape pressed carefully down would probably also go through a copier and be more water proof than an ink jet printer. I just put one piece of tape at the top, but clearly the page could be filled with them. And it is perfectly straight, as printed, I just scanned it crooked :). kathy