Backyard Aquaponics
A place to discuss aquaponics

Hi All,
Just registered and first login. Have been forum junkie over the last few weeks and becoming addicted to the AP idea.
Some of the systems are fantastic. I visited BYAP last week and here is what im thinking!!!!

I have a 2500lt watertank measuring 1.42m diametre and 1.62m wall height that i am thinking of cutting and turning into FT and top half will be turned into GB.
Anyone able to work out how high up to cut it for 1000lt FT? And does anyone think this is a dumb idea?? Tank is HDPE grade.
Any ideas would be appreciated.

I'm no good with pi, but around 0.648 of height should give you 1000 litres.

Personally I'd make the fish tank the full metre, and make the growbed the rest.

Make the FT as big as possible so you can expand in the future, if you are inverting the top to be used as a GB it only needs to be 400mm deep to have a media depth of 300mm for plants. Cutting a 400mm top of a 1600mm tank will leave you with a tank height of 1200mm and a FT volume of 1900L.

You will want a bigger FT at some stage and will be cursing the big chop.

I hope the tank is plastic because not all galv tanks are aqualined and the leaching of zinc can kill fish I have been told.

Hi seamonkey.

Although only new to larger scale projects myself, personally I wouldn't consider making a growbed deeper than about 500mm unless it is absolutely needed for filtration or growing larger plants (read: fruit trees etc). If you're going to create a "simple" system with the floor of the growbed higher than the fish tank then I'd personally be going for something along the lines of:

Growbed:
1.42 (diameter) x .5 (height)
Volume = pi * radius^2 * height = 3.1415 * (0.71 ^ 2) * 0.5 = 792L (approx)

When this is filled with media it will take about 40% of this volume of water: .4 * 792 = 317L of water

Fishtank:
1.42 (diameter) x 1.12 (height)
Volume = pi * radius^2 * height = 3.1415 * (0.71 ^ 2) * 1.12 = 1775L (approx)
With the growbed flooded, this will leave 1775 - 317 = 1458L for the fish, or 82%.

This tank is too high to have the growbed easily accessed if sitting on top of the fishtank, so the fishtank would have to be partially buried or placed at the bottom of a slope, or the growbed placed on a balcony etc.

You don't have a great deal of filtration volume, so using the ratio of 3kg fish per 100L of growbed, you could stock: 3 * 7.92 = 24kg of fish. In the fish tank this would give each kg of fish about 61L of water each: this heaps and will assist the production of good sized fish relatively quickly (little competition for space). If you wanted more fish, you could benefit by adding more growbeds or a biofilter.

The "golden ratios" also recommend to pass the entire contents of the fish tank through the grow bed each hour. If you wanted to have a continuous flow system (autosiphon drains) you'd obviously need a pump capable of lifting 1775L per hour to the height of the growbed, or, if you want to save some power use a bigger pump and cycle it, maybe like:

15min on : 45 min off
15 mins to move 1775L = 7100L/hour pump ! (Too big, too expensive)

so consider something like:
30 min on : 30 min off
30 mins to move 1775L = 3550L/hour pump

Machinate/fiddle/judiciously adjust the numbers to suit yourself, but getting the design right in the first place will make things a lot easier in the future.


Hope this helps, or at least shows a different way to think about the problem?



Scott

Thanks for all the info. I know I will be kicking myself later if i cut the tank and make it to small but I am a bit worried about stuffing up a big tank. I really want GB to be placed over tank also and sinking FT is not an option. I have to come up with a way to seal up top of tank which will end up being bottom of GB as the tank does not have a sealed top.
Tank is a WESTCOAST POLY TANK from Bunnings.

Maybe I should get a system from BYAP and stop trying to come up with a crazy idea. (Just trying to save a buck) Tank was only $700 and would get FT and GB out of it but I dont want to stuff up ratio or I will screw the system up, wont I.?

Have you got a sump? Space for a sump? Have you thought about a two pump system? How much space do you have?

I am still curious how you are going to manage working in / harvesting from the growbed if it's on top of the fishtank! You must be very tall, or have a long stable ladder or other platform to work from? Think SAFETY here, then think about the PITA factor (pain in the posterior).


Scott

Hey Bunson,
The FT will only be 1m high. Do you think I should make it smaller?

I would love to have the FT higher than GB then have sump also but I would be unable to do that without getting a stand built.
I would be able to have sump if I get GB over FT. Im tossing up whether to get rid of old vegie patch and using the space but
I am still at the planning stage really and my vegies are in good health at moment.

PM

Yay!! My brain has been cleared of all crazy plans as I lashed out and bought system from BYAP. My brain was overloaded and after several trips to Bunnings checking out parts and ideas of cutting one of my perfectly good watertanks in half to build system ,I figured it would take me forever and I want to start now..
What a relief when I finally purchased system.
All I have to do now is wait for Wed morning delivery!! I have been out the back, clearing space, much to my vegie patchs disgust.
I have had to pull piles of silverbeet out so I will have plenty of muscle after eating all of it.
Also had to rip out a load of lettuces and Broccolini.
I managed to leave a small patch of originals so I will be able to compare.
Waiting!, Waiting! Waiting!

Welcome... Yes, that was what I did as well. Bought my first system from BYAP, as I did not want to have doubts on why things did not work if I went the DIY way.

I have since put together a 2nd smaller system to trial some of the ideas for a bigger 3rd system. Of which, some lessons where learnt from the 1st BYAP system and applied to the 2nd system.

Anyway, congratulations on taking the step.

Well, if you have not purchased a Freshwater Master Test Kit with the BYAP kit, it is probably a good time to look for one. Search the forum here, I believe there were some recommended internet sites you could get them from.

Thanks Ivansng, I think thats what I will end up doing after I feel confident with BYAP system. Try a few ideas off to the side.
Im glad you say to get the freshwater kit because Carl said I didnt really need it if I followed all the rules but from what I read on the forum, everyone seems to use them. I told Carl that I thought I would feel more confidant if I got one( And Im sure the fish will be happier knowing that Im looking after their home)
May as well have all the fancy stuff. I got a thermometer also just to make sure they are comfortable.
Im itching to begin!!

Well yes do follow the golden rules... with regards to the test kit, I think it is wise to get it, since we all live in the real world and in the real world, things do go wrong... The last thing you want to be doing is to be hunting for a test kit when something is wrong... plus it is unlikely anyone in the forum can provide good advice without test results..

Thats exactly right. No point in wondering what has gone wrong when you can do a simple water test and have the results right then and there. Its part of the fish first aid kit really. I just need some salt and some shell grit to keep on hand and seems that a lot of problems can be solved. I have never dealt with fish before(apart from eating them.YUMMO!) so I dont like the thought of deaths but I expect I will have a few.