Does an air stone actually help the tank in any way?

[Tommy Gun]

Not sure if it works much better but as the waterfall dumps right over the pickup, it seems like a good idea.

IMO and IME, this is a very good 'trick'. I've never gone as far as to alter the intake of an HOB filter but I've always made sure that I keep the intake for my cannister filters as far away from the return as possible. While tank size and depth probably play some role in its importance, I also agree that pulling water from as low in the tank as possible is a good idea for a couple reasons, to include that it may hold less O2 than the water above it. Obviously, as the filter pulls in water, it is replaced right away so in theory, I guess it would be ok to say you are pulling dissolved oxygen down.

Another thing to consider here is that gas exchange also occurs in HOB filters prior to it falling back into the tank. In fact, I believe this is one advantage of the bio-wheel systems. Anyways, while it may be better, there really isn't a huge need to have the return flow from an HOB filter splash down into the tank because it doesn't take a whole lot of movement for this exchange to occur (e.g. think of how little movement is gained by having bubbles from an air stone pop out of the water). I point this out because I've noticed that a lot of people do not enjoy hearing water constantly.

 

[haykay]

nice point and great discussion!

 

[Sombunya]

I also agree that pulling water from as low in the tank as possible is a good idea for a couple reasons, to include that it may hold less O2 than the water above it. Obviously, as the filter pulls in water, it is replaced right away so in theory, I guess it would be ok to say you are pulling dissolved oxygen down.

That's a good point. I will lower the two pick-up tubes down close to the gravel soon. Might even help to pick up more of the waste down there.

 

[Telek]

I can say by way of direct observation that air stones do something good for the tank. Back when I started I had a large turtle in a 30 gallon setup with a pitiful hang-on filter (max 50 gal). I did mention I had just started, right? Anyway the water would frequently turn green, but after adding an air stone within a day it was much clearer. I surmise that it did, in fact, increase the O2 in the water which helped with the aerobic bacteria to clean everything up. Similarly the stone was knocked out one day and within a day the water was greener again.

Later when I was a little wiser I had a 75 gallon tank and used to keep about a dozen goldfish in there (in addition to 3 canister filters enough to handle 800 gal of fish) for the turtle to snack on. I needed the air pump for something else one day so I took it out and noticed that within a day the goldfish were mostly staying in the top third of the tank. I observed them like this for 2 days, noticing that they seemed to be "breathing faster than normal". I then added the air pump back in (connected to a 24" bubble wand) and within 1 hour they were back to swimming all over the tank and "breathing normally". I assume that, again, the O2 was higher in the upper level of the tank, but after turning the pump back on it caused a net gain in lower dissolved O2.

Now if you think from a purely surface area perspective the thousands of air bubbles do actually double or even triple the total surface area that the water is exposed to, so it will increase the gas exchange from that perspective alone. Note that the smaller the bubbles the more surface area and the longer the bubble stays in contact with the water (larger bubbles rise faster). Using a smaller airstone is actually better in this regard that using a larger airstone, however the smaller bubbles also reduce the vertical movement of water, so it's a mixed blessing.

There are, however, 2 more important facts: One is that it promotes vertical water circulation in the tank, helping to churn up the water, and 2 (equally as important!) it promotes air circulation ABOVE the tank. In a lot of setups (especially when you have a complete lid on your tank) the air above the water level is very stale and doesn't circulate so it gets in equilibrium with the tank water rather fast. Having air pumped from outside of this area into the tank injects a lot of "fresh air" which greatly helps the gas exchange.

 

[Indo]

I agree with you 100%. I saw same thing, if I took out the air stone fish would come to surface for air or hang out near top. So I stuck it in hob filter Penguin 200. They say the benificial bacteria live in the filter and like oxegen and what not. Works fine for me.

 

[Roberz00]

***off note*** Who fired up the way back machine?? wow this started way back in 2004. *** surprise mode off***

 

[Telek]

I did a search and this thread popped up so I figured I'd share my knowledge

 

[HooKooDooKu]

...... promotes air circulation ABOVE the tank. In a lot of setups (especially when you have a complete lid on your tank) the air above the water level is very stale and doesn't circulate so it gets in equilibrium with the tank water rather fast. Having air pumped from outside of this area into the tank injects a lot of "fresh air" which greatly helps the gas exchange.

I'm suprised this isn't discussed/mentioned more. I only recently got started with an aquarium, but this was the exact reason why I have an air pump on all my tanks. I already knew from some simple reading online that air stones directly do not add O2 to the water (they do so more indirectly by helping to agitate the surface). But I have not seen much discusion about the idea that in a tank with a hood practically sealing the tank, the air above the water line must surely get stale (educated guess, not direct measurement). But with a pump forcing air into the tank, there should always be a steady supply of air to help increase O2, or even CO2 for those with planted tanks w/o CO2 injectors.