# Determining Flow Rate Of Box Filters

#### H2O Concierge

##### Valued Member
I like the idea of a box filter as an additional filter. I'm sure this is a stupid question. I realize that I can regulate the air output of the pump which increases or decreases flow, but how can I approximate the flow rate through the media. I'm trying to increase anaerobic BB and I was going to put Denitrate in it and wanted to keep flow rate below 50 gph. So I guess I am asking what 50 gph output of bubbles look like? I feel idiotic asking this.

#### KinsKicks

##### Fishlore VIP
Not silly at all! Although, you won’t be able to tell by the bubbles lol. What you can do it have a gallon container on hand. You can either all the HOB go siphon the gallon water, or empty into a gallon container (I prefer the latter)

Then, you time the time it takes for the secondary container to fill with one gallon (or if you choose thr first method, how long it takes for the container to drain of one gallon) Do some quick (see below!) for gallons/hour

If that doesn’t make sense, I’ll be glad to do the math for you

#### H2O Concierge

##### Valued Member
Thank you! Got it. I guess that I just need to modify the way you would check a power or canister filter's gph output. 2 buckets...1 with water and the other empty. Place the corner box filter (bubbler) in one bucket attaching a longer hose on it's output and run it into the empty bucket. Finally, determine the amount of time that it takes to empty 1 gallon out of the bucket. Although I will be modifying it's contents, this is the type of box filter that I will be using in addition to my canister and HOB. It is so hard to find a decent filter under 50gph...so this is what I came up with. Thanks again.