Waterfall - enough bubbles?

Hi folks,

I will be going hydro for the first time ever soon, yay!

I am considering doing a waterfall with 1 small pvc elbow of 5/8 inches (16mm) in a 40 gal tank (DWC). I have a couple options for the waterfall:

1) Using a water pump of 792 GPH
2) Using a water pump of 396 GPH
3) Using a water pump of 317 GPH

I have a few questions:

1) Considering this is the only thing that will be moving the water, which water pump would you use?
2) Would this be enough to avoid the need of using an air pump and stones?
3) Is there such thing as too many bubbles?

I would appreciate your help

Thanks a lot !

Water falls are a powerful form of aeration. If dome with enough circulation, at least as good as bubbles. The same for flumming.

The key to understanding aeration is the fact that oxygen is slow to penetrate deep into a body of water. The very very thin top layer of any body of water will quickly reach 100% DO when exposed to air. Im talking a few micron thick and very fast. But the rate of penetration slows drastically as you get deeper into the water.

Take a cup of water in a tall narrow glass and it might take a few 1/10ths of a second for the top few microns to reach 100% DO, but maybe a few hours for the bottom of the container to reach 100% DO. Take that same cup of water and put it in a very wide, shallow container and it will all reach 100% DO much faster. The shallower it is, the faster it will reach 100%.

This means wide shallow rez will reach 100% DO faster than the same volume of water in a narrow tall rez - no matter how you are doing the aeration.

Its a question of surface area of the water being in contact with the air. This is why lots of bubbles work. each bubble full of air has some added surface area over what ever the container already has. Plus, those bubbles refresh the surface of the bucket as they rise. water from the bottom of the bucket replaces water on the surface as it roils.

Thats also why waterfalls and simple fluming also work. They constantly expose fresh layers of water to the air.

So the key is the turn over rate of the surface of the water.

A 5/8 pipe sounds small to me for a 40 gal rez, so I would go with the larger pump. Actually, Id go with a bigger pipe, but your limited by the fittings on the pump.

I could go up to 13/16 with the 792 GPH pump, would that be enough?
what about the elbow? Is that the best option or should I look for something like a manifold to spread the splash?

Another alternative is to put a second waterfall. However, wont that create a problem with the water temperature?

FYI, the tank shape is like a vault. Wide and short, not really tall (about 20-22”).

DO is dissolved oxygen. The thing about a waterfall is that is relies on the temp of the water to a degree, since it cannot create bubbles that rise up under each plant. To elaborate, the amount of o2 water can hold is inversely related to temp, so you can easily reach a solution temp that will not hold enough oxygen across the entire size of the dwc container.

You can bypass this by releasing bubbles directly under each root zone.

Another thing to consider is (other than cost) why would you want a water fall creating aeration over something like this? (I am in no way affiliated with this product or company selling it, just using it an as example)
It only uses 40 watts and is 35 decibels. It uses almost no power, you can hardly hear it, and it lasts for years.

I never heard of that one in particular but my concern with air pumps is the noise, the tent is in the living room. 220v of that one in particular take 2 months too (European).

I would guess that 35 db is quieter than a waterfall.

hydroplasticsinc said:

The thing about a waterfall is that is relies on the temp of the water to a degree, since it cannot create bubbles that rise up under each plant. To elaborate, the amount of o2 water can hold is inversely related to temp, so you can easily reach a solution temp that will not hold enough oxygen across the entire size of the dwc container.

Click to expand...

I'm sorry, but I disagree with most of that..

Temp and DO are not directly related to water falls or any other type of aeration. The temp is what ever it is independent of aeration type. True that cold water holds more oxygen, but so what? if you dont aerate cold water the DO % will be lower then if you DO aerate it. The same applies to warm water.

No type of aeration is dependent on temperature to work or not work. They all work on cold or warm or hot water equally well.

Secondly, you will never have different amounts of DO across any body of water unless it is stagnant. As long as it is mixing - from a pump, or bubbles or a water fall or flumming - the DO will be the same in every part of the bucket or system. Thats a result of that slow rate of solution of oxygen into water. Its the reason we do active aeration in its various forms.

hydroplasticsinc said:

You can bypass this by releasing bubbles directly under each root zone.

Click to expand...

No. If anything bubbling increases water temps because the pump is putting warm air into the water. And again - every part of the bucket will have the same DO unless the water is stagnant - which it wont be if there is bubbling or flumming or a water fall.

hydroplasticsinc said:

Another thing to consider is (other than cost) why would you want a water fall creating aeration over something like this? (I am in no way affiliated with this product or company selling it, just using it an as example)

Click to expand...

One advantage of a water fall is it can be driven by the same pumps that already in use in an RDWC system. Plus, water falls put LESS heat into the water than air pumps.

As far as noise, the larger the pipe size for any given water flow rate, the lower the noise. You dont even really need it to "fall" very far. You can also try your idea of the manifold. Just have the outlet T off into a manifold and have several outlets. Each one will have only a part of the total flow, so will make less noise.

Again - aeration works by increasing the surface area of the water that is exposed to the air. All you need to do is have the surface of the rez refreshed as quickly as possible. Faster makes for more noise, but you really dont need to go over board.

If the water fall turns out to be too noisy for your living room, change over to fluming. It is just as effective. To flume, just have the pump outlet at the bottom of the rez pointing UP so the pump output roils the surface of the rez. You can actually just sit the pump in the bottom of the rez and point the outlet at the surface. if you do that, I would think the smaller pump would be fine. Or you can just use the return pump you already have in your system.

You do need to be sure you rez has fresh air available and is not 100% sealed. It doesnt need to be wide open either. Oxygen diffuses through air really fast - especially compared to water.

Maybe I didn't do as good of a job as I could have, explaining what I was trying to.

With the temp thing, say you have a 60 gallon dwc tub, 28" x 48", the kind you get at a farm supply place. Here's what I observed, I'll let you draw your own conclusions. With a temp "too high", when I aerated it using any method in just one spot, (like say one end of the tub) without a lot of water movement, only that one spot would have undamaged roots. The water was not be able to hold or carry the oxygen across the whole area, (especially with multiple large root masses blocking it) unless you significantly move the water, (which, yes, a waterfall does do, to a degree) I had multiple airstones spread across the floor in each tub, I think I had maybe 12 of those long wal mart fish tank airstones. What I found was if they moved around and ended up not being directly under a plant, or an airstone directly one under became clogged, those roots would sustain damage. Now if I dropped the temp down to where it was able to hold enough dissolved oxygen, like into the 60s, I would not have that problem. I could move all the airstones to one corner of the tub if I wanted.

Eventually I got rid of the airstones for a type of pond aeration setup. The pump uses maybe 100 watts, (obviously you would not need an air pump anywhere near that size for a single 40 gal dwc setup) and I do cool that air before it enters the tubs. The air comes out of the pump and goes through a small radiator with a fan blowing across it. But water pumps put heat into the water too, especially if they are submersible.

Ah, ok. Thats a different situation than the OP was describing. He is talking about doing the water fall in the control bucket - no roots allowed and no blockages or restrictions to the flow.

hmmmm on second read, maybe Im the one who misunderstood. I ASSumed the water fall would be in a control bucket in an RDWC setup, but maybe not? If this is a 40 gal tank with several plants in it, then some more details and planning will be needed to avoid the situation you described.

Good info in this thread, switched from airstones to fluming or waterfall more than 5 years ago and never looked back. If you really want optimal/high DO you have to inject it from tanks anyways, so were not going for getting maximum O2, just enough to create healthy plants. Waterfall/flume circulates + aerates, and can be T'ed off from the main pump if setup properly while still giving adequate levels of DO.

Id run the 396 in 40gal, thats what I do in my 50 gal. Using 3/4" tube. the 792 would be better, but in summer itd be too hot without a chiller.