Backyard Aquaponics
A place to discuss aquaponics

Hi all,

I have some confusion in my mind re: grow bed to fish tank ratio.

I know that it has been discussed many times but I want to ask some simple newby questions to clarify it in my mind because I am getting confused/

Many times people have mentioned that there ideally needs to be a 1:2 ratio.

If I put this into figures, if I have a 10000ltr fist tank, does that mean that I ideally need 5000ltrs of grow bed or is it 20000ltrs of grow beds? 5000 makes more sense to me but some of the posts have given me the impression that it is the 20000ltrs that are required.

Also, is the ratio focused on the amount of gravel that you are using or the number of plants that the system will support? For example (and going to extremes) if I had a 10000ltr fish tank but got a rainwater tank for the grow bed then the growing area would not be very big because the tanks are tall and narrow?

I am in the process of designing a concept commercial system that I will be posting here once I have bedded it down so I am seeking to clarify some points.

Thanks

Simon

I'll reply but take it with a grain of salt till someone that knows chimes in.

It would be 10000 fish tank: 20000 growbed.

This would allow for maximum stocking densities in the fish tank, but is not neccessary if you have few fish.

The growbed acts as your biofilter for the fish tank so the more fish you have the more growbed you need.

The bacteria live on the gravel and such and you have to have enough bacteria to convert the ammonia produced by the fish into nitrates.

Nitrate also need to be removed by the plants you grom. Some plants will take more than other some on the front it is really a balancing act of sort.

Fish make ammonia growbeds convert it to nitrate and plants absorb the nitrate.

Hope I didn't confuse you further, and that my info is accurate.

Best of luck,
Steve

yep
take it back to the smallest numbers for ease

100L fish tank needs 200L growbed when stocked at maximum capacity of 6Kg of fish

This is the absolute maximum stocking rates for very experienced operators.

For beginners it is recommended that you start out with maybe 1L fish tank to 2L grow bed and about 1 - 2Kg fish.


So, for your 10,000L fish tank you should have up to 20,000L grow beds and about 100Kg fish.

Very good Clovis... yes the ratio is 1:2 fish tank:growbed for maximum stocking densities....

Many operate at closer to 1:1 ratios but also operate at a more manageable stocking level, and one that's commensurate with the age of their system and level of experience......

The total surface area available to plant will obviously decide the total number of plants capable of nutrient uptake, and the type of plants at any specific time will have a bearing on the amount of nutrient uptake....

Having said that.... the number/size of your fish and amount you are feeding will also influence your choice and number of plants at any one time.... obviously if you only have 100 tadpoles which you're feeding a couple of grams a day, you're not going to be producing the same amount of nitrates as a situation where you're stocked with a hundred 500gm Silver Perch chewing you arm off every time you go near the tank....

Like wise seasonal influences like available sunlight hours, temperature will dictate the type/number of plants (and possibly fish)....

Water temperature will dictate fish choice, feed/growth rates etc....

In the end it's all about acheiving a balance.... in the end that balance is probably acheived by time and experience....

To acheive a level of commercial production and to garantee production to suppliers will require the ability to measure, control and adapt all the factors above.... a totally controlled environment....

This means space, time, money, staff and expertise..... and probably lots of it.....

Good luck.

Ok, that has cleared up the ratio, but now it makes me wonder.....

If I am pumping 10000lts into a 20000ltr grow bed in a F&D scenario, how much water will I end up with for my fish to swim in when my GB is full?

Depending on what type of media you are using in your GB, your draw down will be somewhere in the 25-40% range at maximum flood.

And that is what has caused my confusion!

I couldn't get my head around having such a high GB ratio, but that ratio does not take into account lower water because of the bulk being taken up by the GB Media.

So this means, if I am looking at a commercial system with maximum stocking densities, if I have a 10000ltr fish tank I need a 20000lt GB which ideally has a grow media that reduces the water volume down to 25%. That means at the maximum it would use 5000ltrs of water to fill the GB.

That means that I would need to calculate my stocking densities on 5000ltrs as that is the low point of my fish tank levels once the GB has been filled.

Is all of that correct or have I missed something?

BTW, all of these figures are hypothetical atm. I am just using these numbers for my own clarity.

And whether or not you're using a sump... sump size.... pumping from sump or from tank.... etc....

You'd be using a sump tank system of one sort or other regardless I suggest Simon.... so the growbed capacity is equal to the sump capacity...

It's kind of like a reserve..... additional capacity.... but you don't need to include it to calculate your stocking densities...

And remember you're probably not going to start with max fish and/or max growbeds anyway....

If you are.... good luck...

Psycho, for something that large, it is better to be flooding the GBs in sequence rather than all at the same time...this way only the volume of water in one GB is removed from the fish tank

also don't forget, profile of your tank will impact greatly on the "perceived" low tide.

If the tank is taller than wider then its low tide will look lower than if the tank was wider and shorter


but at the end of the day it will still be the same number of liters.........just rambling really

I agree with everything, all of the time, except for the above (sorry to be perdantic) but you COULD have up to 20000L grobeds, not SHOULD.


No, calculate your stocking densities on the total amount of water that is circulating in your system, not just the amount of water left at low tide.

There are alot of benefits of having a larger tank and less fish including a more stable temperature and generally easier to keep in balance.

Agreed there. Have a look at VB system and see how to keep your fish tank level at full all the time by using a sump which will hold the entire flood cyle water. Also, I think you will find the figure for most mediums (and certainly the case for 14mm drainage gravel I use) would be closer to 40% water 60% gravel. ie in a 1000 litre gravel growbed, you would need 400 litres of water to fill it.