Backyard Aquaponics
A place to discuss aquaponics

My set up is a few weeks old and running well enough but I know I do not have the growbed volume I will eventually need. I understand that the ratio of growbed volume to fish tank volume is 2:1. Since the gravel in the growbed is meant to provide a home for the bacteria as well as to give support to the plants, my question is this:

Will it affect anything if I achieve the proper growbed volume but make the growbeds deep rather than wide? I know that this would affect the number of plants I would have space to grow. I would have the correct amount of gravel but most of it would not be supporting plants. Will it affect the balance of the system? I read somewhere, perhaps on this forum, that it is preferable to have undersized planting area than undersized surface area for bacteria.

A second question I have is related to the material that supports the bacteria colonies. If I am not using that material to support plants, does it matter what the material is? In the world of ponding, many people use bio balls, chopped up plastic, scrubbies, etc. to provide homes for their bacteria colonies. Surface area is the key issue. If I have a 100 gallon fish tank, one hundred gallons of gravel with plants and a 100 gallon tank of lightweight material that will support bacterial colonies, will that do the trick?

Thanks for your help.

Rand

Rponda

Bacteria need oxygen, so providing you are getting sufficient oxygen to all the gravel (ie no anoxic areas) ok. They will build up sludge though then possibly problems. Using a bio filter as an addition will convert to nitrates but again has the cleaning problem. It all depends I suppose on fish stocking/size densities, higher you go the more nitrates to be removed by plants.
The ratio's are only a guide (my opinion) too many variables to calculate it accurately. (probably get flamed for that one )

no, the ratios are only a guide. Every system is different, depending on the tank you can get, the grow beds you can use, the animals to provide the poo, the plants you are growing, your physical location and climate, the pump/s you use, the plumbing you use, whether you go Flood & Drain or continuous flow.... The list goes on. Sometimes you just have to suck it and see

Nope, no flaming for a fair (and correct) opinion, Sleepe. I am successfully running a system that is 1:1 -- that's all the more growbed I could squeeze into the sunroom. I have heard of systems running even more growbeds--maybe 4:1. The trick is to do what you can, and then observe your own system and your own habits to learn what your limits are. So build what you can, Rand! Some of us do run with biofilters made out of scrubbies or bird netting, for example.

btw Sleepe, RSG filters take advantage of anoxic areas--in fact, they create them on purpose to offgas excess nitrate or to chelate iron in place. Even anoxic bacteria can be good in moderation!

I have a sneaking suspicion that people might be over thinking the amount of gravel needed for bacterial colinisation

Trust me, or don't , that in any system with a gravel growbed the surface area for bacteria is probably 10x more than is needed.

So bacically this leave us with the ratio (as a guide) for there two factors............

1) Amount of given plants you can grow

2) Amount of volume for solids filtering and subsequent mineralisation.

Number one is highly variable depending on what plants you grow, which leaves us with number two

i have had succesive crops of high density plants in a standard bath tub filled with gravel. Its now approx T=1.5 years and im going to pull my bed down for a good clean out

did i have any probs with bacteria? nope

did i have any problems with nitrate? nope (well only inbetween plantings )

would i have liked to go another 2 years without cleaning my bed, yep!

SO IMHO, the ratios are VERY VERY flexible. you're never going to have probs with bacteria. If you go deeper you will probably have higher points on the solids score card but lower on the amount of plants you can fit in, ans vis versa.

Steve

I found from my system, even though i had the ratio around the wrong way 1:2, I was fine because i used very low stocking density. My water quality is good, i never got any peasoup stage at all either.

glad you posted all that steve, you may have just made my life much easier

Cheers

no worries, sticked the thread too for good measure

So which way are you saying it varies? If I have a larger surface area, I can have less depth?
Can I go below the 300mm that seems to be the golden rule? or is that my minimum depth?

Thought it was pretty clear

300mm seems to be a good MINIMUM depth.

Deeper is fine and will give you greater solids capability

Deeper to make up the volume may leave you without enough surface area to plant plants and hence nitrate problems

KP,
I started out with about 12cm (tight vertical restrictions in window obstructions (dw) *grin*) and found that if you plan to have the surface dry (for less algae) and figure the bottom few cm is probably going to stay too wet for roots it leaves very little space for roots and good growth. A deeper bed gives a nice layer that stays damp, aerated, and stable temperature. The 30cm bed I have now is far far better.

RP,
I think the limiting factor for the growbeds is having enough space to grow enough plants to use the nitrates, so it is more a matter of the amount of waste the fish make (a function of feed quantity) vs plant growth. A better guideline might be fish:growbed rather than fishtank:growbed. As folks have pointed out before, if you have too much nitrates, plant more. If you have too little, add more fish (or feed more if they will take it or pull some plants that you don't care about).

Or throw in a little vermicompost on top of GBs if fish not grown enough out yet to give enough poop production? What you think?

I don't know about throwing the worm castings on top, I usually put them right where the water flows into the bed so they will spread around and be useful to the plants.

As for the depth vs Surface of beds vs surface area of media, etc. Remember that the bio-filter needs surface area that gets wet, doesn't dry completely out, is relatively dark, and gets plenty of air (either from flood and drain or from supplemental aeration.) People have found that 30 cm or about 1 foot is a reasonable standard minimum depth for grow beds. It allows for some gravel on top to stay dry and reduce the algae and evaporation, there is space in the bottom for the water that never completely drains and there is still enough depth for plant roots. 30 cm provides enough depth for good bio-filtration with flood and drain, it is also a good depth to make auto siphons relatively easy to set up.

I think the 2:1 ratio is perhaps a guide for those who will stock near max fish tank capacity and use gravel or other media in 30 cm, flood and drain beds and have a sump to absorb the level fluctuations, this ratio should give plenty of bio-filter as well as enough planting space to keep the water quality good and nitrates in line even when a bed needs to be harvested and re-planted.

Deeper flood and drain beds will provide more bio-filter but don't allow as much planting space. There are options open where a system has plenty of bio-filter but not enough plant space. One can add NFT, DWC, or tower plant growing locations using the water that comes out of the gravel beds provided the plumbing for that can be arranged.

Note that the type of plants grown will greatly affect the amount of nitrates used up per a given plant space. Like spinach will use more nutrients than will lettuce, Tomatoes will use more than peas.

Or grow something like pumpkins that trail far beyond the growbed.


SOB!!!! So that is why that system has green tomato plants and all else is yellow! Where are my pruning shears?!

Thanks TCL! As usual great advice. So much to think about.....

I will then put the vermicompost there instead. I think I like the idea of a deeper GB - 50cm - because of the accomodation of bacteria stability and extra height of plants that can be grown cos more anchorage. (I love papaya and bananas. I will start them here only probably and then move them outside when hardier and taller. Might even start litchi.) I am using free bricks and have tons of free gravel media so going to go for it straight off. Being so new to AP I will just keep putting in vermicompost until the fish grow out enough to support all the plants I want. I like the idea that I can micro-manage it a bit till I see how it all works.