Aerating HOB vs Tank

[Webjaker]

Cory recommended adding an air stone to the HOB filter, but in the forums, a few years ago he argued against it. Please give me your reasons for/against air stone in HOB vs in tank?

[Tony s]

I usually add an extra sponge filter instead of an airstone. That way I have a fully seeded sponge to start a new or quarantine tank if needed. An airstone after the impeller in a hob would work fine, but you wouldn't want it before that, or right at the intake tube, you could easily lose the hob's prime that way

[Tanked]

I don't have any feelings one way or the other. 

On the for side:  Some people don't like bubbles at all, and an air stone inside the OB would eliminate those bursting bubble leaving water drops and minerals everywhere.  It would also improve the overall appearance of the tank

On the against side:  The air stone inside of the HOB might be a wasted effort.  The bubbles inside the HOB might not be in contact with the water long enough for the oxygen to be absorbed.  An air stone outside of the HOB provides some additional surface agitation and water movement especially in a potential dead zone

[Webjaker]

On 10/14/2024 at 10:37 AM, Tony s said:

I usually add an extra sponge filter instead of an airstone. That way I have a fully seeded sponge to start a new or quarantine tank if needed. An airstone after the impeller in a hob would work fine, but you wouldn't want it before that, or right at the intake tube, you could easily lose the hob's prime that way

I have intake sponge and another sponge and filter rings in HOB.

Asking specifically about the air stone added to Hob instead of in tank, as suggested in Corey's video

[Tony s]

On 10/14/2024 at 11:06 AM, Webjaker said:

Asking specifically about the air stone added to Hob instead of in tank, as suggested in Corey's video

right, but like I said, it should work fine. As long as it's after the pump. My only other thought, it could cause a lot of bubble popping in a less protected area. possibly splashing out of the hob 

[Pepere]

I seriously doubt an airstone in a HOB does much of anything…

the HOB already has plenty of surface agitation in the fairly tiny amount of surface area of the water in a hob.

To run it in a hob, dont you have to reduce the amount of filter media in the hob?

most of the aeration benefits of an air stone has little to do with the air bubbles in the water column.  It is the popping of bubbles on the water surface that creates the increased gas exchange…

and an air stone in the tank is causing some upwelling of water in the tank increasing water flow that you lose by sticking it in a hob…

[mynameisnobody]

An airstone in a hob is the same as in the tank, not better or worst. If you’re curious, place one in and see what happens. If you like it then you’re good, if you don’t then move it. You’re overthinking this a lot. 

[knee]

I wouldn't even bother with an airstone if you're already getting good surface movement from the HOB. But IMO it's a waste of time to add one unless your HOB retains the water longer inside the filter for the bubbles to be of any help. 

[Bubbletrouble]

An airstone in the HOB makes no difference to the oxygen uptake. As stated, it's the surface agitation which allows for gas exchange between atmosphere and water. If your HOB creates enough surface agitation and current within the tank, no airstone would be needed, neither in the tank nor in the HOB. I ran my tank on only the HOB for years. If you think there is not enough agitation, lower the water level to make the HOB water returning to the tank fall a longer distance. Another option would be to glue some plastic shapes into the path of the returning water to make it break up more before it returns into the tank. I did that with a cheap HOB and it worked really well.

[Odd Duck]

There is very, very little benefit from surface gas exchange within the actual bubbles.  It’s the water lifting effect that moves water to the surface or pulls it through a filter that gives better gas exchange.  I love to run HOB’s plus sponge filters in tanks because I position them so the flow they create runs the same direction. I want the entire body of water in the tank to be “rolling over” from bottom to top along one edge (or side) and it will flow across the top for max surface exposure and gas exchange, then back down the other side, and sweep across the bottom, then rise back to the top.  Getting water to the surface and preventing stagnant areas is my goal for all my tanks. I don’t always achieve ideal for every one of my tanks since some are a bit experimental.