Backyard Aquaponics
A place to discuss aquaponics

Ok so I searched around and it seems that in an AP system with gravel GBs there is no need for a biofilter or solid separator. Is this true? After researching some larger systems on the web, I see that all are running a pretty large biofilter system.

Is it needed? I was just curious. my system is doing fine without it.

no need depending on your stocking to GB ratio.

The GB is your biofilter.

most commercial AP systems are nft, so they need to filter the solids to prevent clogging in the channels or anaerobic zones developing in their bioballs from a build up of solids.
Stocking rate as dt says is key. Commercial recirc aquaculture is geared to 100kg per cubic metre water as an example. If u were running high densities of fish and have heaps of gbs, I would still be looking at some sort of drum/screen filter prior to bioball trickle tower in the return line.
In home AP systems, some solids in our fishtanks isn't really an issue bc of low stocking rates. In commercial setups solids are a time bomb waiting to happen, lotsa fish alive one day, all dead 2-3 days later.
I don't know ur budget, but u prolly should consider uv and ozone as well in ur screening process. If u run ozone, make sure it is post bio but not the last process in line prior to water re-entering ur fishtanks. The ozone needs time to degrade from 03 to 02 otherwise it will burn ur fish gills.
Lotsa things to consider. Keep reading and planning.

Removing solids removes trace minerals.

And as DT says, the GB is your biofilter.

Yep, just gets back to what is the commercial requirements, fish or garden produce. If fish, ur water needs to be spot on, if garden and lower fish density, gbs as ur bio would prolly be fine.

You have to remember that, as TT suggests most cases where the commercial emphasis is the fish not only employ biofilters, but solids and protein skimmers (often dumped to waste) and regularly changed out, and usually dump, a large percentage of the system water each day.

The beauty of AP is that it is essentially a closed loop and the vast majority of the system compnents are used and reused over and over...

damn this forum rocks! Ok thanks guys. I'll stick with the GBs as biofilter.

I will be teaching an AP course next year and the school wants a medium-large system so I might look into a seperate biofilter.

Off topic, does UV kill the good bacteria too? I would think not so good for AP systems?

UV kills everything

HN, this link might be of interest to you ...

http://www.lanikaifarms.com/

Even here they use a bio-filter.... probably most of the ones that do and the ones you've seen... are based on the UVI, fast flow, floating raft style.

You'll notice none of them use gravel beds.... we do

Yeh UV kills everything man. No need for it in a home system but must have in a commercial setup, same with ozone. For me there are ethical issues, but if my wallet was on the line commercially I would prolly use both.

Thanks rupert, I want to visit lanikai farms next time I'm in Maui. Looks like a pretty cool place.

Please explain!

Does UVI use them?

sorry, thinking about Australian commercial RAS when I typed. I would be prepared to bet a large amount of someone elses money that u could not walk into a commercial recirc setup in Oz and see either or more likely both.
I reckon UVI get away with it bc of the tolerance of tilapia to suboptimal water, the relatively short growout time as the fish are reasonably small when harvested. I would be amazed if they had the same success with,say,silvers at those densities bc of the longer growout period and higher risk of issues. We will prolly never know, so moot point I guess.

In my brood tank (Tilapia hatchery), I have an aquarium pump/filter which has bio-balls and some fibre (fibreglass?) in it. My nutrient levels remain low and the growth in the GB is pitiful. I can germinate seeds, but little growth thereafter. The pump is on a 15:45 on:off cycle. There are around 14, 60 - 90 mm Tilapia in there as well as ~200 fry. I am feeding around 50 gm of home made fish food daily and all is being eaten. Additional floating fish food (~20 3mm balls) and a flat hand of duckweed (what stays on my hand when lifted from under duckweed in duckweed buckets) are added to see how hungry the fish are. The fish food is gone by morning and about half of the duckweed remains next evening.
My sump is a large bio-filter, but the pump there keeps the water level low enough to prevent significant bio activity (I hope)

I feel that the bio-filter part of the pump is causing the nutrients to be dissipated before the GB can take advantage of them.

AM I on the right track?

To test my theory, I have replaced the pump/filter with a pump and will monitor the nutrient levels for a while.

Does anyone have any suggestions on other probable causes?

Regards,
Tony