I use a Reef-Filler peristalic pump. It has a max output of 3 Gallons per Day, built in redundancy! I use it to top off my entire tank and all of my topoff water goes thru my Kalk Reactor, so even if it gets stuck in the on position due to float switch error, I'll have some time to catch it. It has settings so that at 100% output it pumps 3GPD, but can be turned down to as little as 10% output. It can pump a good distance ( like 100 feet) so locating it far from the tank also possible. I've also been using it for over 5 years so it's quite reliable. The only real downside is that this pump is basically $200 new.
Hope this helps,
Dave