Backyard Aquaponics
A place to discuss aquaponics

So...every dog has his day. I've been driving by a concrete company for about a year now, and finally called about a large poly tank they had sitting in their yard. Turns out they didn't want it, and even better would let me have it. This is a 2500 gallon vertical tank. Dimensions are appx 9.5 feet high, and 5.5 ft wide circular. Now, the questions: Is it better to use the tank as 2 -1250 gallon circular tanks, each about 4.25 ft high or cut the tank lengthwise and make 2- 9.5' by 33"? Is 57" to tall for an FT? I know circular is better, but what about surface area? If I did go long cut, I could also slope the tanks slightly to have solids drain at one end..I think. I would need to use the Bobcat to back-fill under the sides if lengthwise and then need to do something to stabilize the dirt.Or build a retaining wall around as I backfill. If I had 2- 1250 gallon tanks, how much of a sump would be ideal? Just thinking about adding my ever growing Tilapia "herd" for now, but with an eye to expand for GB and DWC in the future. Sorry for all the questions, but want to get it right the first time. Also have on hand: 1- 265 gal IBC, 2- 450-500 gallon fiberglass spas, and several 55 gallon barrels. Thanks guys!(and ladies)

Since you are in a hot area, i would personally cut it into 2 circular tanks. If you were able to do trout i would cut it length ways and have 2 trout runs.

But then as you said, if you cut it length ways you could use one as a GB, the other could be multi use (dwc/ FT, etc).

I think the amount of work you are willing to put in may be the dictating factor.

Thanks Yavimaya. No trout here. Work is always a factor, but I will put in the amount of work needed to do it right the first time. I'm not interested in building the prettiest system, although I give huge props to some who build furniture quality GB's and FT's, I just want highly functional, highly effective, and as easy to maintain as possible without breaking the bank. I would like to do Koi in 1 bed. Have purchased some Koi and they need a new, bigger home. Nothing too special from what little research I've done, but should do better in the Winter and maybe provide a small income as they reproduce. Trying to get the tank set up right, and then figure out the GB/DWC at a later date.

Congratulations on your score.



This statement indicates to me that before you make a decision you should get a better handle on how solids get moved around in FTs.

http://www.backyardaquaponics.com/forum/viewtopic.php?f=8&t=22254&hilit=fish+tank+design

In my situation I would keep the tank intact because I'm short of water storage space.

good score, use it wisely.

Thanks Stu. I understand the solids removal in a round tank vs raceway design. But having said that, still wonder if a slightly angled circular bottom wouldn't do a better job then a traditional flat bottomed rectangular FT. My assumption would be that the solids would settle in the low part of the bottom of tank and then make their way down toward the low end? Is this incorrect? Would an SLO in the circular tank be more efficient? Due to the height of the tank, it would be difficult to put a bottom drain without building a stand and then having to build a platform around the tank to service fish. Neither seems like a good option. Open to suggestions, what would you guys do with the design?

Nope. You can actually have the floor slope up towards the center and the center drain will still work and the solids won't collect around the lower outside edge.


Yep.


Yep.


The recommended minimum ratio of width to depth is 3:1. Since the tank is 5.5' wide to get that ratio you would have to cut the tank ends down to 1'10" which would be kind of short

Hatchery tanks maybe

There are a lot of AQ tanks sold that have a 1:1 ratio but I don't see them recommended in any places.

Sorry I don't have any useful suggestions.

So maybe the 10' long by 5.5' wide option would be better? Then surface area is no issue. I can use a slightly larger pump if needed to maintain circulation and ensure the SLO/ bottom drains work. More work, but seems like a better option.

I wouldn't do it.

I once had the option of getting a mold for a trough 2.5m across 8m long and because it was semicircular 1.25m deep. As I learnt more about tanks I decided to give it a miss.

Maybe I'll go a 2.5 to 1 and only lose a little bit on each tank. Extra aeration should makeup for less surface area.
Could use it as a giant sump and wait to find a circular 2000-3000 gallon FT.

Surface area isn't the reason for the minimum 3:1 recommended ratio of width to depth.

what is?

Narrow or "silo" tanks have big problems with the water not mixing evenly.

In tanks that are 3:1 or wider you get two currents forming or rather one current that has two parts.

A radial horizontal circulating current and a tangential vertical circulating current. The current are formed by the combination of the force form the inlet jets and the friction of the water against the BOTTOM of the tank. If the tank is two narrow there is not enough friction to cause the self cleaning radial and tangential circulating currents.

Ill use the tanks vertically and add the horizontal and vertical inlet jets like Timmons suggests. May not be perfect, but with my tilapia and Koi, it should work, and a lot cleaner then my spa. Thanks.

When you are dealing with limited resources you have to do what you have to do and often it is not ideal.

Having said that Timmons also says that a lot of people have had a lot of problems with "silo" tanks and that the extra volume of having them tall tends not to be usable because significant volumes of these style of tanks don't mix evenly which leads to areas of water with low DO concentration and high TAN concention.