The Litremeter pumps are awesome. Stay away from these:
http://www.marinedepot.com/ps_AquariumPage~PageAlias~dosing_pumps_top_off_aqua_medic_SP_3000_sp3000_niveaumat_reef_doser.html">http://www.marinedepot.com/ps_AquariumPage~PageAlias~dosing_pumps_top_off_aqua_medic_SP_3000_sp3000_niveaumat_reef_doser.html</a>
They work OK for about a year... I would not reccomend them for continuous use...