Gph Measures In Externals Vs. Hobs

[Rynofasho]

One thing I've noticed in looking at externals is that many of them make claims to be able to filter very large aquariums, however they output much less GPH than some HOB filters that claim less filtering ability.

IE, I have an AC110 -- good for 110 gallons, and the GPH claim is 500GPH

I'm looking at a Rena Filstar XP3 instead -- it claims it's capable of filtering a 175 gallon thank, however GPH rating is only 350GPH.

Can someone explain this discrepancy to me?

 

[Rynofasho]

Bump

 

[BigbruiserAl]

GPH and the abilty to sustain a bio load are 2 diff things. A canister will hold more surface are for bacteria to breed on thus making it suitable for a larger tank. A hob may have a Higher GPH though but not as much room for bacteria

 

[waterdrop]

Agree with BBA, media volume is a more powerful factor than flow rate. The colonies have room to spread out and more debris can be held between cleanings. You are also adding more water volume to your overall system, if you think about it, thus giving your fish a larger tank in a sense.

It is also important to separate the marketing statements about how many gallons the filter can support from the technical specification of the actual flow rate. From the flow rate you can see where you stand with respect to the typical 5x turnover average we often recommend as a planning starting point (reasonable ranges often go from 4x up through the 10x or above that planted tanks have.) The "gallons handeled" type statements are usually coming from the marketing guys.

Another decision factor between HOBs and EC filters is noise. External Cannisters can be totally silent, like Internal filters, whereas by definition an HOB will have water noise at the surface.

It can be a hard decision sometimes as the AC filter (AquaClear) are quite good for the money, giving you a very general rectangular media space that you can customize quite easily, just like a good EC filter. In the end it is a personal decision, you just have to weigh all the factors. Each of these types is just about as quick to remove to the cleaning sink (the HOBs just lift off the tank and the modern EC filters just unclip from their hoses.)

WD

 

[moochy13]

i think theres a thread in the hardware section where people are comparing described flow rates with actual flow rates. most externals flow rates are given with no media in the filter. add media and the flow rate takes a severe drop off, i think up to 50% i saw in the thread.

 

[waterdrop]

i think theres a thread in the hardware section where people are comparing described flow rates with actual flow rates. most externals flow rates are given with no media in the filter. add media and the flow rate takes a severe drop off, i think up to 50% i saw in the thread.

Good point. The companies are always trying to help make the numbers look as high as possible (and, to be fair, to take out factors like different types of media, that make variable differences.) It is supposed to be pretty standard practice to take the numbers with no media in there and no extra pumping height beyond the recommended height.

Beginners always have this extra thing to learn, that despite their initial planning, the filters nearly always have less actual flow and there is always room for miscommunication (between manufacturers, shops, customers, hobbyists) because of some people taking this into account and some not.

Getting the right overall amount of flow and the right circulation patterns and then maintaining those over the years is something I've come to dislike a fair amount as I find it to be pretty tricky. There can be a LOT of factors when you bring in the preferences of different fish species and the needs of different plant situations. It ends up being trial and error and learning.

~~waterdrop~~