How many gph do I want?

in a 40 gallon tank?
I would say a filter rated at 200 minimum. If you have many fish or any large fish going in the tank go up from there. A heavy fish load or several medium to large fish would need as much as double that or 400 GPH.

wat does gph stand for?

thanxx 4 the points
at least 200 Gallons per Hour preferably more
What does GPH stand for?
The most common rule-of-thumb regarding gph is 3-4 TANK cycles/hour. Keep in mind that most filters advertise the DRY gph, meaning without media, bags, etc. So adding this stuff will decrease the actual gph somewhat. It's much better to overshoot than underestimate, so I would go with about 160-200gph. All you should really need for filter media is the fine foam and coarse foam. Carbon help polish water and remove impurities, but loses its ability to do so in a very short amount of time. If you're using a canister filter, there are ceramic chips that are good also. The key is to have enough water flow to "clean" the water, but allow it enough contact time with the biological media to promote bacterial growth. This will help to more quickly convert the fish waste to less harmful forms.
A good rule of thumb is to buy a filter that turns over the water at least 3-5X/hr. So, for example, since you have a 40 gallon, you would need one that rated from 120-200 gph. Personally, I would buy one that was one step higher than the maximum here if you could afford it as most people tend to overfeed their fish (I'm not saying that you will), and so it gives the tank that extra kick in the filtration department.
As many as you can afford to buy. What Ryan said sounds good too.
Depends on the fish, too. For messy fish like oscars, the rule of thumb I've seen is turnover of 10 x per hour with hang-on-back filters and 3-5 x for canister filters and the like. But 5 x or so for more normal fish like tetras and stuff sounds reasonable. I always go up at least one size from what the box says. My biowheel (rated for 50 gal) does 200 gph on my 29 gal tetra tank and it seems more the adequate to me.
My recommendation is to always filter 5-10 times the tank volume per hour what ever the tank size. You can adjust this depending on stocking, activity level, and waste production of your fish. If using multiple filters, the combined gph of the output should equal 5-10 times the tank volume (not 5-10 times each). So for your tank, a total of 200-400 gph is suggested.
I have a large reef tank that is turning over 20+ times an hour...

The answer really is in what kind of animals are you going to keep in your 40g set-up? If it's a saltwater reef tank with SPS corals- you better shoot high, but if it's a tank with mainly fish (or all fish) that are smaller and/or delicate- you do not want to blow them around too much...

Hope this helps!
I've always attempted to achieve 10x/hour water circulation. In your case that would be 400gph. That would allow some extra bioload just in case u happened to have one fish too many in the tank. Penguins or an AquaClear would be a nice choice for that tank.
Depends on what you're planning on keeping?
If my Seahorse tank was turning 8 to 20x the volume of the tank I WOULDN"T HAVE SEAHORSES ANYMORE.LOL
My REEF tank turns about 20X.
For Large fish or fish from fast rivers you can go to 10-15X
For Guppies this will probably blow them away or suck them out of your tank.
Get an adjustable filter and adjustable powerhead and play With them until you get the MAX flow that won't kill your fish and will keep them happy.
The powerhead can be placed where the current will keep the crap suspended in the water until the filter picks it up.
What are we talking about here. Everyones assumed a filter which you really dont have to look at GPH most brands will say its meant for this aquarium(if your tight on cash get a 40 gallon filter if not try for a 55 or 60). Now if its a pump it all depends on how much of a current you want flowing through your tank. If its a UV sterilizer it depends on the wattage. For mine (9watts) i go down to 45 gallons per hour to kill parasites. Please specify though i think its a filter in which case you have good answers already.

Related Questions and Answers ...