When is it a good time to finally add water to top off an evaporated tank surface? How low should the level drop? Is there a standard number of inches below the top edging of the tank?

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MARINELAND 60 GALLON HEARTLAND ENSEMBLE - NEW!
DUAL DELUXE FLUORESCENT HOODS (24"X2) - 48" X 13" BLACK HEARTLAND STAND 40009
AQUEON QUIETFLOW 55 325GPH (X1) - HAGEN AQUACLEAR A620-110 500GPH (X1)
TOP FIN AIR-8000 (X1) - PETCO BUBBLE BARS (18"X2) - APC SurgeArrest System
FANCY GOLDFISH (X4): Common Orange Fantail (1) - Red Cap Oranda (1) - Silver/Gold Ryukin (1)

This depends on your system. A lot of hang-on filers make a lot of noise if tanks aren't full to the top. On the other hand if you want Mystery Snails to lay eggs, you need a space of at least 8 inches. Jumpers have an easier time of jumping out if the water is at the top. To cut down on evaporation and eleminate jumpers you can cover your tank.

It's basically up to you and what you want really. If you don't like the level low or the noise it creates when lower, then add more water. As for me, I normally let it drop about a gallon. Just makes it easier for me when it comes to adding fresh water. I can hook up a jug and let it drip in slowly without worry.

As for this, 2-3 is actually plenty of room ;o)

Thanks guys.

And to the first responder, my tank is covered.

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MARINELAND 60 GALLON HEARTLAND ENSEMBLE - NEW!
DUAL DELUXE FLUORESCENT HOODS (24"X2) - 48" X 13" BLACK HEARTLAND STAND 40009
AQUEON QUIETFLOW 55 325GPH (X1) - HAGEN AQUACLEAR A620-110 500GPH (X1)
TOP FIN AIR-8000 (X1) - PETCO BUBBLE BARS (18"X2) - APC SurgeArrest System
FANCY GOLDFISH (X4): Common Orange Fantail (1) - Red Cap Oranda (1) - Silver/Gold Ryukin (1)

I've encountered situations where you don't want to let your tank water evaporate to a level that puts your heater out of the water. This could lead to overheating the tank, breaking the heater, or other bad juju

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FW 10G, 5 neons, 1 fancy male guppy, BNP, pond snails, ~80 RCS. Camboba, java moss, java fern, willow hygro, ludwigia repens, dwarf sag, anubias nana. AC50, 50W heater, Current USA Nova Extreme 2x18W T5HO.

"Give me your penchant and I shall grant you deliverance." - Falcor

I don't have a heater. Well, actually, that's not true -- I have a heater, but it's not in my tank at the moment because I have goldfish.

But I'd be worried about letting the level drop beneath what is safe for my filters -- I once did a water change where I didn't unplug the filters first, and my Aqueon started making a coughing-and-dying noise before shutting off because the water level got too low (the filter is self priming)...I don't want the water level to get so low it does that again...

__________________
MARINELAND 60 GALLON HEARTLAND ENSEMBLE - NEW!
DUAL DELUXE FLUORESCENT HOODS (24"X2) - 48" X 13" BLACK HEARTLAND STAND 40009
AQUEON QUIETFLOW 55 325GPH (X1) - HAGEN AQUACLEAR A620-110 500GPH (X1)
TOP FIN AIR-8000 (X1) - PETCO BUBBLE BARS (18"X2) - APC SurgeArrest System
FANCY GOLDFISH (X4): Common Orange Fantail (1) - Red Cap Oranda (1) - Silver/Gold Ryukin (1)