Q: What is the maximum height in feet? I currently own one that goes to 4 feet but need to buy a replacement and have considered buying this pump
A: This is the original pump that comes with the filter. If you have the original pump then the pumping height is the same.
FYI - They don't list that info on the pump because it is not relevant in this application since the pump sits in the aquarium and only has to pump up a few inches over the rim of the aquarium to start and maintain the flow through the filter. No priming is a main advantage of the unit.
Q: I have a 770 filter, the pump pumps just a small stream of water, I cleaned the filter good but still doesn’t pump much, I am using it on a 50 gal fresh water tank, I guess it’s big enough?
A: I am not familiar with a 770 filter made by Rena. If you are outside the US it is probably a filter we never sold in the US and RENA France is long out of business.