Backyard Aquaponics
A place to discuss aquaponics

You pretty much have that right on, but nobody really knows what the formula would be for the difference. Also you need to consider the pump size. If the pump is 4 x bigger for the 15:45 compared to the CF for the same volume bed, then the filtration should be about the same. However the CF bed seems to do slightly better due to water retention time aiding nitrification.

There is also solids to consider, I don't know which one deals with them better. Perhaps CF because there is a longer period of time for which to capture the stirred up wastes. Then again the larger pump might be able to capture more.

Anyway, for all practical purposes there is not much difference, especially if you don't over stock your system. I have been understocked from the beginning of my system and I haven't had any problem with great plant growth. Actually I'm thinking the normal stocking densities don't apply to trout; stock lower, trout poop too much.

To confuse things further....

Many systems are run flood and drain and constant flow rather than flood and drain and timed or dosed flow.

However I dont think the flow is the primary limiting factor in a gbs ability to deal with waste. Rather it is oxygen. In the BYAP trials the systems are relatively lightly stocked and there fore the oxygen demand would be relatively low. In systems where they are heavily stocked it is likely the the flood and drain constant flow gbs will out perform the constant flooded constant flow gbs but no one has tested this yet.

....

Could that be because they were operating below their capacity in terms of fish load and so would not see any real difference.

I would fairly confident that the trials did not show how much capacity they had to manage a fish load.



As a general question, what is meant by filtering capacity. Would a given filter (ie grow bed) volume that has twice as much water passing through it have more filtering capacity than one of the same size with only half the amount of water passing through?

I have 2 ornamental fish tanks inside that have been operating successfully for over 15 years. Both are relatively heavily stocked. one has a high volume of water passing through sponge filters that hang on the side of the tank and the other has a large Eheim canister filter sitting outside of the tank that has a very low volume of water passing through. Both are highly effective (although the sponges need cleaning more often) in filtering the water but use different filter volumes and water flow rates to achieve this. Unless I'm missing something I would have thought that the same would apply to our situation.

any thoughts on this?
cheers
Marc

I think trying to put an exact formula to ratios is not going to work. We all have different media in the growbeds, and different depths to area of growbeds, and different pumping rates and timing.
Some have worms in there growbeds which help a lot, some dont. Different climates will determine how efficient the bacteria will be. Ph levels will also make a difference to the bacterias effectiveness and some folks cant get there ph down below 8 due to the media in the growbeds
Probably many more things as well , but, I reckon, stock to a medium/low level of what is recommended and see what happens.
You will in time get to know how YOUR system handles things

was it 3kg of fish to 100ltr of growbed, this has worked for me as a safe rule. (thats if I got that right?)

Yeah thats been said but my system in the greenhouse that is the only one that has given my crops of fish, would not have handled that load
Yours might

I think there is no doubt that what everyone is saying is right. I guess what I'm trying to get to the bottom of and understand is which of the systems (flood and drain, constant flood etc) provides the potential for the most filtration.
It is a bit like speed. Consider the analogy below

You can do 100km/hr in a Barina with not much left for overtaking and it does the job well.

You can also do 100km/hr in a Commodore with a fair bit left for overtaking and doing the job comfortably taking on the hills along the way with ease.

Then you could be doing it in a Torana GTR XU1 (showing my age) it will also do 100km per hour but with so much in reserve etc etc.

The fact is they all do 100km/hr and by just observing that parameter they could all be considered as equal, and they are as far as doing that speed (this is like saying we all are successful with 3kg/100l of grow bed or 25 fish per BYAP bed). But some have greater capacity to deal with problems along the way and the added burst of speed that may be needed. It could also be argued that their capacity is also greater.

Overstocking is a problem, there is no doubt of that but would people be less likely to get into trouble if they passed more water through the filter beds than they would on a 15min on 45min off system. From the BYAP trials it would seem that, in the main the plants don't care.

Joel, perhaps the next trial could be to see if there is any difference in stocking capacity between the systems? Just kidding.

The point of this debate is not to ratchet up the stocking rate but to increase the buffer as I would much prefer to be running down my Aquaponic road in a Commodore (or an XU1) than a Barina.

Cheers
Marc

To use your own analogy... the Commodore and XU1.... have more capacity... to use when necessary...

When everything else is equal (ie... 100km/hr)... there's no real difference...

Same with a system.... it's a matter of filtration capacity... for when it's required.....

If your "barina" of a system is stocked/fed to the maximum of it's capacity.... it's not going to matter that much if you turn the lights on, or toot the horn...

Filtration of biological or solids? If we are talking about the same depth beds with the same media and volume, then flood and drain will have more biological capacity and constant flow would have more solids filtration capacity.

And when you are talking about ratios you mean the amount of water that the fish tank will hold compared to the amount of water the grow bed will hold (displaced by the growing media). As opposed to how much liquid each empty container would hold. Right?

Usually the ratio refers to empty volume:empty volume. After the grow beds are full of media they will hold approximately 1/3 the volume of water.

Great. Thanks!

Very few systems don't have enough biological filtration physical space capacity in fact I don't really know any. This is the amount of area that bacteria need for habitat to process huge amounts of amonia and nitrite. In any system there may not be enough bacteria to process the waste present but this is a cycling or management issue rather than one of a the biological filter being too small. In systems with gbs the biological filter capacity (ability to provide habitat for bacteria that process amonia and nitrite) is way over sized but the solids filtering capacity is the limiting factor and as we see regularly on the forum is often undersized.

The filtering capacity of a gb is dependent on three things first the ability of the gb to capture the solis and retain them within the gb (filtering capacity), the second is the rate at which water can flow through the filter (flow capacity) and the third is the rate at which the ecosystem of bacteria, microorganisms and invertebrates can process the retained solids (processing capacity).

The first and second are dependent/limited by the physical characteristics of the gb ie volume, design, constuction and media. The third is principally oxygen limited.

The amount of flow that a gb can handle is dependent on its physical characteristics but its capacity to filter is generally indepent of flow. For example a sand filter may be able to have a high rate of flow but have very limited filtering capacity and be prone to clogging if its capacity is exceeded. A column graded media filter (big pipe stacked with succesively finer grades of gravel) may have a large filtering capacity but only be able to except a relatively small flow.

The amount of oxygen available to the ecosystem of a gb is mostly dependent on the amount of flow and the concentration of the oxygen in the fluid (water or water and air). A constant flooded intermitent flow system would have the least oxygen. Where as a flood and drain constant flow system would have the most oxygen available for the biological activity of the solids filtering or more properly the processing of the retained solids.

In a well designed filter there will be enough filtering capacity to retain the solids, enough processing capacity to process the retained solids and enough flow capacity to ensure that the solids are removed from the fish tank much faster than they are produced.

Understanding all this is really only necessary if you are designing building comercial systems. The best solution for backyard systems is just add more gbs or have less fish. While adding another gb or gbs may mean more expense and space but it will be far cheaper in the long run.

And having less fish enables you a greater capacity to deal with any issues that can arise, mechanical failures, excesses of nutrient or temperatures etc... Where as maintaining higher stocking levels in the same given amount of water while increasing growbed volume means you walk a tighter line..