Backyard Aquaponics
A place to discuss aquaponics

Hi there,

and another new member here from Perth who 'Stumbled' across BYAP on Gardening Australia, and then bumped into Joel at the Open Garden a bit later... I Love It!!!
My system is a 1000lit tank with 1x 60l recycling bin and 1x 200lit kiddy-pool.
and this relates to my question:
I would like to have more plants growing, especially after reading that the GB to Tank ratio should be ideally 2:1 (this is the first question, should it be 2GB : 1 Tank, as in if I have a 1000lit tank, should i have 2000lit GB, or the other way around?)
but now the real thing:
I was thinking about how to manage the waterflow from tanks to GB if i have more GBs, but where do i get the water from? as in when my GBs are full (assuming that i have 1000lit GBs) my fishtank is empty... surely something i would like to avoid
is there some kind of contraption that enables me to flood and drain one GB after the other? I could not think of any... I always come back to the worry: what if one day my contraption malfunction and my Tank gets emptied...
Anyways, i would be greatful for some advice, and look forward to hearing from you'all
Happy fishing!

Hi Kaihawaii....

The 2:1 ratio is growbed-vol:tank-vol..... to explain.... it's not fixed in stone or law

The ratio is both probably pretty much a guide to the maximum amount of growbed volume that a given tank volume can sustainably support.....

and a guide to the minimum amount of growbed volume required to support a maximum stocking density of around 5-6kg/100ltr.

In reality AP is as much an art as a science and no two systems are alike.

In real terms no beginner with a new system should try and stock any more than say 3kg/100ltr => fish mass:tank vol.

Controlling the amount of water drained from your tank is acheived by several different system designs and methologies....

From continuous running pumps and auto-siphons.... timers and bell-siphons... to CHIFT PIST systems (Constant Height In Fish Tank and the Pump In Sump Tank), where the water remains at a constant height in fish tank.....

Regardless, it's almost universal to utilise a sump tank... a reserve volume of water in a sense....

I'm not an expert, I am about to regurgitate much of what I have read on this forum, I don't even have any fish yet myself.

I believe the ratio is 2:1 Growbed:Tank So yes 2X the amount of Growbed volume. Do remember that this is if you are stocking the fish tank at max capacity. Many people don't stock at max capacity and thus a much lower growbed volume can work. I have heard that many people are running something more like 1:1.

This brings us to how can you flood your grow beds without leaving your fish high and dry. First a grow bed filled with media takes less water to fill than empty. The exact amount may vary but 40% might be a good starting point. So if you had a 1:1 ratio and a simple system with a grow bed the same size as the tank, when the grow bed was flooded there should still be 40-60% of the water still in the fish tank.

Ok, but how does one do this with a 2:1 ratio? Yep, there is the rub. I suppose this is where people start messing with other ideas like, sump tanks, header tanks, multiple pumps and timers, Alternating flout tanks, actuated valves, cascading grow beds.

It is not an easy answer as far as I know. I am kinda searching for an answer to that myself. I think the most common way to deal with it is with sump tanks. But then I've also noticed a tendency for people to stick more critters in the sump.

Another way to get more media working for you without sucking up huge volumes of water in flood and drain would be some constant flow or trickle beds/troughs. The biggest challenge here seems to be even distribution of water so that the media can function to support bacteria (if sections of media dry out too much or stay dry all the time, they are not really doing their job.)

Some people also set up a "filter" there are not any plants growing in it but splashing a large amount of water through a bucket or barrel of media can do a lot to improve water quality and the nutrient rich water can then flow through say NFT troughs.

Hi KH, Welcome!

The device in question is a Sump Tank. The fish would of course greatly prefer that you avoid emptying the tank of water, too. However, given a 2:1 ratio of growbed:tank, and maybe a 33% use of water to flood beds, you are potentially left with about a 33% filled fish tank if you flood all beds simultaneously. You can either use a sump tank as many do, or stagger the fill of multiple grow beds. That's what I do. I have 3 growbeds and only about 1:1 ratio. The growbeds fill at whatever rate they wish, and drain after the water level kicks off the autosiphon. Usually I do not have all 3 filled at once. Even so, my water level only fluctuates about 100mm.

Wow, nothing like a highly active forum to get you more answers than you needed in 24 minutes flat!

If you want to distribute water to growbeds one after the other (and after reading the above posts you may no longer want to) there are a couple of options.

Valves
Valves are difficult, because we work with such low pressure. 0 Pressure activated valves, such as actuated ball valves, or direct acting solenoids are generally too expensive or too restrictive to flow (cheaper models)
You can doctor your own valves if you like. Some people are using car door actuators, or doctored sprinkler valves.
Unfortunately, it is not commonly needed so not many ppl are looking into it.

pumps
Buy a couple of pumps, and plumb each to a different set of beds. Then turn 1 on, then the other using a timer or some such.

cascading
I'm looking into draining one growbed into another. So is CRTreeDude. This is completely untested as yet, and I wouldn't advise a newby to consider it.

Welcome to the forum BTW :-)

A problem we run into with timers is if one malfunctions or if they are slightly different you may end up with bot in sync rather than staggered.

One really nice system configuration has a tank overflowing into growbeds draining into a sump. This way your tanks can never empty. There is a whole discussion on drilling holes in tanks along with a clever overflow device that acts like a hole in your tank.
http://backyardaquaponics.com/forum/vie ... 190#104190

The growbeds provide conversion of ammonia>nitrites>nitrates and a space for plants that remove excess nutrients (esp nitrates), so if one has too few nutrients one will have weak/yellow/slow plants. 2:1 is safe for any reasonable stocking rate, but might not grow plants well if you are light-stocked. I suppose one could have the growbeds partly empty and plant more as nutrient levels build up...

Anyway, this is a great place for anyone who enjoys fish, water, plants, and ideas! Welcome!

Good point Hydro. I missed that warning, as I've never had more than 1 pump, I never learnt that particular lesson.

A rank novice, dare I mention that my ratio GB:Tank is 1:35?

But take into account that at the moment I have only a couple of kg of fish in my "tank" (a 75,000-litre swimming pool). But I have plans to grow at least enough to end up eating fish twice a week. This target still only needs an output of say, 100 - 200 kg a year. Add the likelihood of a fast-growing circle of fish-eating friends who'll consume another few hundred kilos, I am hoping that my pool will prove to be enough of a buffer. I am prepared to replace quite a lot of water as I intend to irrigate the large (organic) garden by using nutrient-rich pool water (which is becoming clearer and clearer--I hope to swim in it again soon).

Unorthodox but fun!

Adrian

julies is currently 1:150

My hydroponic beds have a volume of 299 gallons. When flooded my 250 gallon nutrient tank is still almost 33% full.

Oh and welcome!