ok, my opinions differ. i shoot arowanas a lot.
cpl are of zero helps. esp if the glass is thick.
at the meusuem, try shooting at a longer exposure and getting as close as possible to the exhibit, use a monopod for support. ok taken that that's often not very possible, then use a flash. flash can cause reflection, but u can diffuse or shoot it at an obsure angle. standing at an angle might help, but then it would take quite a bit of trial and error.
with fishes, the opposite applies. u can't get close cause the fishes will be frighten, esp those in fish tanks. so i normally shoot at a distance of 1meters, tripoded and pendicular to the tank. this helps to cut down reflection, avoid shooting at angles. and make sure the tank is amply lit. top light above tank is best, or light from within tank. else u can use a flash with diffuser, bounce it off the celing. however, all this dun appy at public aquariums, with those just snap away. light is good and fishes are deaf to ppl.
try this forum for fish shooting tips,
www.arofanatics.com