Ok this could be a repeat thread but I tried the search & could not find any. From my experience I know that HOB filters will outgas a fair amount of CO2 from Planted tanks. I have read this & personally observed this using calibrated ph meters & regency test kits. To me that is a con.
Depends on how low the water line is.
However I also know that having a gas exchange of some kind at the surface is beneficial as well, meaning more O2 being brought into the aquarium. That is a pro!
Plants also add oxygen to the water. In a planted tank, I don't believe surface agitation is needed.
I also know that HOB filters tend to scum up the surface know matter what you do but this can be minimized. That is a con!
Not true. HOB filters actually break up the protein and bio-films through surface agitation.
Another Con can be additional flow agitation on the surface can cut down on par reaching lower levels of the tank. That my friend is a con!
I can't comment on this, as I haven't done any measurements. I can see refraction causing issues.
They do offer good organic filtration but semi poor bio filtration. This would seem to be a tossup.
Organic filtration? I know of three classes of filtration used in the aquarium hobby:
-Chemical (Carbon, Purigen)
-Mechanical (Removes crud from the water)
-Biological (Converts Ammonia to Nitrate)
I have always had good bio-filtration with my HOBs. It is a function of the quality of the filter and the exposed surface area of the media.
I run pressurized CO2 in 1 tank & DIY in another & from what I can see is that in the DIY tank the tank seemed to do better when the little Eihiem 2211 was backed up with the HOB filter. But the penalty was maybe losing a day or 2 in the fermentation bottle from the extra out gassing of CO2.
The yeast in the bottle will produce regardless of the CO2 concentration in the water. They don't shut down at 30ppm. Thusly, whether you had an HOB, no HOB, or if the CO2 line came disconnected, the amount of time the bottle was producing gas would not change.
I have a low flow problem in my pressurized tank that I feel the HOB filter would help but I might have to crank up the CO2 a lot to help counter the CO2 discharge from the HOB filter! Some may say just point the spray bar up but that I find causes a lower flow problem down low.
So go get a re-circulation pump. Looks like an underwater fan. A HOB filter will only create flow in the area directly in front of it.
Abstract: What is everyones opinion on using HOB filters in high or low tech applications? Thanks.
I use an HOB by my canister inlet. It is the filter that runs my surface skimmer (another great way to deal with surface scum).