Backyard Aquaponics
A place to discuss aquaponics

Hi there,

I'm having issues with gunk settling in my GBs. The net effect of 18
months of fish poo and probably too much food is that all my 3 gravel
beds are needing a good clean. The latent amonia in my system is very
high apparently caused by the gunk in the beds. So high that if I
don't do something fish will be endangered. Currently my ph is 6.4
temp is 24 and amonia is about 8. So things are ok but won't continue
to be as the water heats up.

Cleaning out the beds is prooving to be a back breaking task.

So to prevent it happening again I'm trying to decide what sort of
filter I can add to the system to best clean out the solids.

My system is simple, an inground pond 3000l with a laguna 9000l pump
up to 3 600l gravel GBs. The GBs drain into a 90mm pipe which returns
the water to the pond. There is no sump.

I currently have a UV light installed between the pump and the GBs
that I can turn on if algae becomes an issue.

I am considering what sort of filter to install. The options I am
considering are either a radial flow filter made from a blue barrel or
some sort of commercial canister filter.

The things I'm worried about are that if I install a blue barrel then
it needs to be installed in parallel to the gbs and as such not all
the water would pass through the filter. This way I'm worried solids
will still accumulate in the GBs.

With a canister type filter then it can be installed between the pump
and the GBs and all the water will pass through it.

Does anyone have an opinion? Any recommendations on canister type
filters that can be inlined? I'm thinking about a cheap jabao cbf1500
but not sure what other options to consider.

Thanks for any advice.

You don't say how many fish you have in the system?

the first option would be to add more GB, or reduce fish feed rate.

Don't know anything about the "jabao cbf1500" but if an inline filter blocks up it could be catastrophic for the fish?

Hi,

I have about 90 smallish silver perch. about 10cm and smaller.

I guess if it clogs up it could be a problem. Checking it regularly would be the go. The chances are that I would notice anyway as the GBs would get no water.
As for adding more GBs it's not an option as I'm out of space.

I can reduce fish numbers which would help some.

I still think some sort of filter is required.

How much food are you feeding daily with that setup (max and min values ) ie summer and winter.

How big are the grow beds?

I was feeding about a cup morning and night. That is when the water is warm in winter less, not sure but less than half as i recall.

The beds are 600l each. So 1800l total.

Right in the cusp then of 1 fish per 20L, so not overstocked per se. I haven't had to use filters (apart from employing something to clean dust from media) so take my advice from a grain of salt haha. RFF's very good at pulling larger solids, and not too high of maintenance. Canister type high chance of blockage if not checking constantly. Why can't RFF be employed currently, I didn't fully understand that. RFF followed by canister if possible would be best bet. Of course, first option would be to install another GB if possible?

2 cups a day wow, that is about 225gms!

for 90 small fish that is a lot of food.

assuming your fish weigh 75gms each you would have 6.75kg of fish this is the Dr Wilson Lennard calculation:-


As its off the scale because of your feed rate, note recommended daily is 1 to 2% of fish mass I raised the fish density to get a 2% feed rate as its more dependent on the feed rate!

Slowboat, I get the gist of your post, but as I am blind I can't see that png attachment. I'll see if I can find someone to help explain it to me.

Also because I'm blind it's possible that my estimation of fish size is incorrect . They are fingerlings that were added to my system in April of 2012. So they have grown for 18 months.

It is quite possible that they are bigger than my estimation. My wife is well, let's say, not the most accurate when describing fish sizes . I do know that as one would expect they are of different sizes.

I'm just going on the idea of feeding them what they will eat in 5 mins. The food is floating so I can tell if they eat it all or not. If they don't eat it all I cut back on the food.

Is this not the correct aproach?

To answer the earlier question of why a rff filter can't be
installed. Yes it can, just not inline with the GBs. I have
only a FT no sump. The GBs are above the ft so I pump from the
FT up to GBs which are flood and drain.

My understanding of a rff filter is that I would need to return the outflow back to the FT and couldn't have the full flow of my 9000l pump through the rff then on to the GBs.

So I picked up a cheap canister filter last night. It has a UV light built in to it. I'm planning to plumb it in place of my current UV light. Then I can filter the water to the GBs.

I'll also install a rff filter by splitting the water from the pump off to it.

This means I'll have:

- pump goes to both rff filter and canister filter.
- rff filter returns water straight to FT.
- Canister filter continues on to GBs and then back to FT.

Hope that makes sense. I can't draw diagrams .

the PNG file is an image of a spreadsheet.

the spreadsheet is a calculation by Dr Wilson Lennard,

the calculation says the GB required to process your feed rate is 36.6m² at 300mm depth.

the fish size is not that relevant, it is the feed rate that has the greatest effect.

Would you consider reducing the feed rate? one cup per day would be plenty IMO.

Hi,

So you are saying that the issue is that even though the fish eat the food, the GB doesn't have enough ability to process it?

36sqm sounds like a lot of gb. I have roughly 6.

Are you certain that that is in meters not feet? As even if i drop it to one cup a day then I would still need 18sqm?

Hi Crazytree, one product you could try is Lysofos, I think that's the right spelling? it is used for aquaculture to eliminate sludge and anaerobic build up in ponds, it is basically good bacteria that eats decaying organic mater, it does work well if you follow the instructions, I think I paid $16:00 for 250 grams some time ago, you sprinkle it on the pond surface then stir it in and with in a few days it starts working, I would reduce the amount of feed to half for a few days until you see an improvement.

it is perfectly safe to my understanding by the way but check it out for your self.

Cheers and good luck.

Hi,
I've ;installed the filter last night so let's see if that helps. Have one GB offline while I try and clean it.
Need to get something to block the outlet so it doesn't flow back into the ft.

I'm trying to remove half the gravel, stir a lot and pump the dirty water off with a pond cleaner pump.
So far it is sort of working...

Hopefully I'll finish it today.

Crazytree,
Do you have any red worms in your grow beds to help keep the solids to a minimum? Also it is my understanding that if you run your GB in constant flood instead of flood and drain, it may also help. As your GB media stays wet longer allowing the bacteria on them to do their job continually. Instead if only 15 to 20min an hour. According to the BYAP trials there is very little difference between grow rates in CF or F&D. Plus it is a very cheap option. Just remove the bell on your siphon. Or get a properly sized standpipe. If you are running a timed flood and drain, and the pump can outpace your drains divert enough of your pumps outflow to balance the system.

Yes there are a lot of worms in the gbs
I can run either flood and drain or cf. from time to time I change between them.