Fish Tank Depth

[GaryD]

Hi,

I'm starting to read (more and more) that fish tanks need to be one metre (around 39") deep.

Does anyone have a credible source for this notion?

In the past four years, I've set up quite a few backyard aquaponics/aquaculture systems (about ten of my own) and all of the fish tanks were less than one metre deep.

In fact, the tanks the tanks that I have used most frequently have a water depth of around 600mm.......and I'm wondering if 600mm is OK, why not 500mm or 450mm?

How deep are your fish tanks?

Gary

[Kaduda]

I had read an article about raceways which had said the best was a tank using the 1:3:10 (H x W x L) rule were the most efficient are removing solids...The bottom needs a slight slope for it as well...I will try to dig up the research paper upon that...Though I believe it was from SRAC...

[arachdog]

Without actually reading the sources you refer to Gary I would suggest that the reason is purely to do with temperature stability. The vast majority of indoor aquariums would of course be far less than that, which isn't a problem since they are inside where the temperature shifts about far less anyway.

[GaryD]

Without actually reading the sources you refer to Gary I would suggest that the reason is purely to do with temperature stability.

In which case, overall volume is the issue rather than tank depth.

Tanks are easily covered......and there are several reasons why they should be.....and temperature control is just one of them.

[arachdog]

In which case, overall volume is the issue rather than tank depth.

Tanks are easily covered......and there are several reasons why they should be.....and temperature control is just one of them.

No, because a large shallow tank has a much greater surface area than a smaller deeper one. Hence it will respond to the ambient temperature changes much faster.
But it not just the tank either. You have to look at the whole system, raceways work well because they have a high flow rate and a large sump tank to provide thermal storage elsewhere in the system. Or more commonly are simple flow through affairs.
If you really want to find out how you system is performing in terms of temperature stability the only real way to find out is to log the temperature for a while.

In my opinion a tank cover should be made from the widest mesh that will stop your fish from jumping out. Even with aeration the surface water-air interface is still an important source of oxygen and equally important an exit point for CO2. Trying to preserve heat by sealing the tank top in anyway is a false economy as it will increase your aeration costs, and the extra aeration will also remove heat from the water in just the same way.
At the end of the day the fish need a certain area of water-air interaction, you may as well use what doesn't cost you anything to provide first. So only if all my aeration was off and I still found I had plenty of DO, would I consider covering my tank with anything solid.

[GaryD]

Hi,

No, because a large shallow tank has a much greater surface area than a smaller deeper one. Hence it will respond to the ambient temperature changes much faster.

Not for the tank volumes and the range of tank depths to which I'm likely to commit.

But it not just the tank either. You have to look at the whole system, raceways work well because they have a high flow rate and a large sump tank to provide thermal storage elsewhere in the system. Or more commonly are simple flow through affairs.

If we're talking about aquaponics (as distinct from aquaculture), raceways are a non-event. As for other parts of the system, I advocate bypassing the growing systems in the interests of reducing overnight heat loss.

Trying to preserve heat by sealing the tank top in anyway is a false economy as it will increase your aeration costs, and the extra aeration will also remove heat from the water in just the same way.

That depends on the temperature of the air that you use. In my next system, I hope to trial use of waste heat from our chick brooders to help maintain the fish tank space at optimum temperature.

Gary

[arachdog]

Not for the tank volumes and the range of tank depths to which I'm likely to commit.

Well its mathematically unavoidable. I presume what you mean is that you think its not significant in your design. You could well be right. I was just discussing the possible rational behind the very vague advice you talk of, that recommends 1m minimum depth. I certainly don't agree with it as a rule, because there is so many other factors to consider. But it's probably a good rule of thumb for a simple fish pond.

If we're talking about aquaponics (as distinct from aquaculture), raceways are a non-event.

I wouldn't be so quick to write them off Gary. I can envisage novels forms of aquaponics utilizing raceways.

That depends on the temperature of the air that you use. In my next system, I hope to trial use of waste heat from our chick brooders to help maintain the fish tank space at optimum temperature.

Well then maybe it doesn't apply to you Gary, but I think you'll agree that you situation is quite unusual. I still think the general advice you should be offering is to others is not to cover their tanks with anything solid. Then if you want to be really thorough you can give them the proviso, unless:
A: They are heating their tanks in the first place
and
B: They happen to have a convenient source of waste heat to obtain hot air from, that isn't practical to transmit to the water in any other way.

[GaryD]

Hi Arachdog,

I wouldn't be so quick to write them off Gary. I can envisage novels forms of aquaponics utilizing raceways.

As long as we're talking about flow-through systems, their applications will be very limited because of the way they access public waterways. Even low impact use of a waterway like small-scale hydro power systems will be viewed narrowly by the authorities.

While from an aquaponics design perspective, recirculating raceways present some opportunities, they also pose some challenges.

I still think the general advice you should be offering is to others is not to cover their tanks with anything solid.

Depends on what you mean by the term solid. I'm not talking about airtight but, in any case, a fish tank cover should address the following:

• Prevention of access by toddlers, pets and predators.
• Reduction of heat loss.
• Prevention of fish from jumping out of the tank.
• Eliminate direct contact with the water by sunlight.

Utilising waste heat is just one aspect of the integrated backyard food production (Microponics) approach that I advocate.

Gary

[Sir Lancelot]

I have not yet set up an AP system but reading this i have another situational question. In my housing situation id like to build a 600x600x1200mm high square tank and waterproof it.

I can incorporate a sloped bottom for solids removal and having a high tank would be safer for little ones.
With the small surface area i will probably need added aeration (i guess)

Does this setup send up red flags for anyone?
Anything dramatic i need to consider further?

[Crusty]

I have not yet set up an AP system but reading this i have another situational question. In my housing situation id like to build a 600x600x1200mm high square tank and waterproof it.

I can incorporate a sloped bottom for solids removal and having a high tank would be safer for little ones.
With the small surface area i will probably need added aeration (i guess)

Does this setup send up red flags for anyone?
Anything dramatic i need to consider further?

Really depends on what you intend to grow. If you are growing something the size of gold fish, I see no issue. However, if you are growing bigger fish for eating, then 600mm square is a little tight for swim space. Again dependent on the species but most fish need to swim for heath.

Hi,

I'm starting to read (more and more) that fish tanks need to be one metre (around 39") deep.

Does anyone have a credible source for this notion?

In the past four years, I've set up quite a few backyard aquaponics/aquaculture systems (about ten of my own) and all of the fish tanks were less than one metre deep.

In fact, the tanks the tanks that I have used most frequently have a water depth of around 600mm.......and I'm wondering if 600mm is OK, why not 500mm or 450mm?

How deep are your fish tanks?

Gary

Tanks design is really relevant to the particular species of fish, their behavior and swimming activity. In other words, they are designed to provide equal water quality (multiple tanks), solids removal and optimum velocities for the size of the fish species cultured using hydrodynamics. . This involves some standard width, length, diameter and depth requirement. All of this also depends on the way the water enters and leaves the tank.

There are also velocity requirements (I have mentioned before) for different fish species. Most fish will require around one times the fish length per second for improved growth rates and feed conversion. Round tanks are ideal for this, as higher velocities are achieved easier. (So fast swimming fish are suited to round tanks, slow fish in rectangles.) Though they can spin too fast and fatigue the fish. This is where the depth of the tank plays its part. If the water is too shallow for the fish, the water will be turbulent from the action of the fish swimming, which disrupts the water flow velocity and there by making solids removal very difficult.

For example, a 2.4m diameter tank such as a stock water troughs commonly sold as aquaculture tanks in aquaponic circles, will not be deep enough to effectively remove solids. It is difficult to provide an example for all situations. In the back yard, pretty much any tank will suffice, though your choice will be reflected in how much work you need to do and/or your feed rate and density/growth.

If you are not concerned with solids removal and growth rates, these principles do not apply and you will have to stock much lower densities.

cheers
Paul V