Backyard Aquaponics
A place to discuss aquaponics

Hi all,

I'm currently in the process of building an aquaponics system in San Francisco, CA.

I'd like to get a few opinions (or facts, even) about how to spec it properly.

Here is what I have so far, and some of the questions I have not yet answered:


The fish tank will be the Hot tub. I estimate that it's capacity is between 1500 and 2000 gallons. (5500L-7500L)
It will likely be lightly stocked and also host some aquatic plants.
Question: How much fish should I stock given that the main goal is to feed the planter beds rather than to grow fish?

The planter beds are custom build (already done ) 8ftx2ftx1ft and I have 2 of them. Thus total planter bed volume is about 250 gallons (1000L). Of course most of that volume will be taken up by the growing medium.
I'm thinking of using pea gravel primarily, but possibly supplement with expanded gravel as well.
I'm planning on using continuous pumping from the fish tank directly to the planter beds and have an auto-siphon to drain back into the fish tank.
Question: How frequently do I need to recirculate the water in the system?

here are assumptions and my tentative answers, but please correct me if I'm wrong.
From UVI aquaponics system: "A volume ratio of 1 cu-ft of fish-rearing tank to 2 cu-ft of pea gravel hydroponic media is recommended for flood and drain gravel aquaponic systems. This ratio requires that tilapia be raised to a final density of 0.5 pound/gallon and fed appropriately.)
I'm planning on using trout and/or catfish as the main fish, but I'll assume that they feed at similar rates to Tilapia.
Using those numbers, I suppose that my 32 cu-ft of planting volume only requires 16 cu-ft (120 gal) of hot tub, the rest being excess/buffer. That would mean that I should stock 60 pounds of fish (once fully grown). Is that correct? That seems like a lot.
Does that also mean that, at that stocking density, I can recirculate only 120 gallons of water/hour?

I hope that all made sense, please send me any questions if you would like some clarifications.

Any and all input/advice is apperciated. Thanks

Petrus,

To start off, welcome to the forum. You must have the largest hot tub I have ever seen. Is it possible that you miss calculated? My FT is a 10ft round pool, that is 3ft high. And it holds less than 1500gal. Try this converter tool http://www.pentairpool.com/support/calc ... olcalc.htm Be careful with pea gravel as a lot of it has limestone in it. Personally I like lava rock. It is usually bought in bulk at the same place you can get pea gravel. For your circulation questions. Circulation is more for the fish than it is for the plants. This is why some people use indexing valves. Plan on turning over your FT at least once an hr. I do not see a ST listed. What design are you planning on running? CHIFT PIST is the way most of us here run our systems.

Haha, you're totally right, floridafishin.

I looked up a few models online and it looks like it holds more like 500 gallons. I was way off on the estimate!
You're right that I don't have a ST.
The hot tub FT is surrounded by a deck, so the GB's will be sitting above the hot tub. As a result, I can't overflow the FT directly into the GB. I can't go in the other direction either (ST->pump->GB->siphon->FT->siphon->ST), because I wouldn't be able to siphon from the hot tub without drilling a hole through it.
I'll post pictures soon.

...so I', afraid I'm just going back and forth between the 500gal hot tub and the 250gal GB's.

Lava rocks sound really good, but I heard they float in a flood and drain system. Have you had any problems with that?
I also found this stuff: https://www.youtube.com/watch?v=oYk5UXaRV94
looks REALLY good, but it's also REALLY expensive.
I also considered making some wood char since that has a HUGE surface area as well, but I imagine that would have an even bigger problem with floating.

What's the advantage of using indexing valves vs. just using a T splitter?
I'm planning on using a continuous pumping with an auto-siphon, but I'm having problems finding a bulkhead that can go through my GB's. The growbeds are boxes made of 2x4's and lined with pond liner. Looks like all the bulkheads have a max wall thickness of 1/2 inch, whereas my wall thickness is 1.5 inches.

My local hydroponics store has what they call "ebb and flow fittings".
It looks like how that works is that the taller fitting is just a stand pipe for setting the max water height. The shorter fitting is connected to a pump on a timer, when the pump is off, the GB would just drain backwards through the pump. When the pump is on, the water just wells up until it gets to the stand pipe height and then overflow back to the FT.

https://www.hydroponics.net/learn/build_ebb_flow.asp

So is the hot tub below ground? If it is not why not just inlay the GBs into the deck? And then bury a ST. Personally I would use the bottom drain already in your hot tub to extract the fish waste. A natural center drain. Just plumb to what is already there. Lava rock does not float at all. Has a great surface area. The only complaint I have ever heard about it. Is from people with soft hands saying it is rougher than other media like Hydroton. Indexing valves allow you to run more GBs at a reduced gal per day. Because unlike T's it shuts off water to one GB and starts filling another while the first GB drains to your set height and wait there until it is their turn again. For your bulkhead problem. You should check out https://www.aussieglobe.com/ not only do their bulkheads allow for a greater span. But you also have another option in this regard. You can cut out room a little larger than the bulkhead or uni seal that you choose to use. Bridge the new gap with a thinner board. Then connect the uni seal or bulkhead with just the pond liner and plywood since it is thinner. You will find that a lot of the stuff in a traditional hydro store here in the US is of little value to us. As we generally run much larger pipes. And flow a lot more water. Everything we use is easily built. By the was consider using the CF method instead of F&D. Less parts (cheaper), ease of use, and added water volume are all benefits.

Plus not to mention that inlaying your GBs would allow you to put your pump into the ST so you were not pulling fish waste through your pump and causing extra maintenance and earlier pump failure.

I've attached a picture of the finished system. I have since filled the beds with Lava gravel and have begun cycling the system.

A few notes:
The hut tub is ~500 gallons and is sitting on the ground and surrounded by an elevated deck.
The 2 grow beds are ~125 gallons each
I'm doing flood and drain.
I have the pump on a timer that will fill the beds up to the level of the standpipe (visible in the picture)
When the timer shuts the pump off, the water will drain back out through the pump (backwards).
(the fill and drain hole is visible in the picture just next to the standpipe).
I'm using 3 air stones to add aeration and some river rocks at the bottom of the hot tub for decoration.


I plan on adding:
worms to the growbeds
duckweed, some other aquatic plants
some additional water features (PVC pipe for fish to hide in or something like that)
and
FISH! most likely trout, catfish and possibly sturgeon.
probably some fresh water shrimp as well.

I understand your want to put decorative stuff in the bottom of your FT. I would advise against it because it will diminish the ability to self clean.

Here's an update:

As you can see from the picture there is a LOT of algae growth. I guess that's pretty normal given that it's new system(?)
Is there anything I can do to help get rid of the algae? I'm thinking glass shrimp and Daphnia (and other zooplankton)

As a result of the algae, I can't see the fish
I presume they're still alive given that I haven't seen any dead fish floating on the surface.
I have 3 small channel catfish and 3 Koi in there (hopefully).

My pH is all over the map. It started out at 8.2. Then went up to 10(!) the next week. I added some vinegar to bring it back down to 7.
What's causing the pH to go up? How can I stabilize it? I'm thinking rock dust to add some buffering effect.

I tried adding some worms but they died pretty much instantly. What's the correct way to add worms to the system? Do I need to put them in a a basket with some soil or other substrate?

The cycling looks like it's done at this point: my NH3, NO2, and N03 levels are all at 0 on the test.

I have a few things planted now as well: Kale, beans, peas, tomato, cucumber and broccoli. They seem to be doing ok.
I'd also like to plant some more aquatic plants. I have some Anubias at the bottom in the river rock bed and some floating Egeria. I'm thinking of adding some duckweed and Azolla to help compete against the algae. I'd also like to put some more submerged plants.
What's a good substrate to use for rooted aquatic plants? I guess put them in a basket with wet papertowels or vermiculite or something like that?

anyways, thanks for the tips and advice.

..
I am using those eco-shopping bags.. in clay balls..
I use a square waste bin that is near the same volume.. the bottom cut out...
Flood the bed to make the balls more mobile.. press the bin down... remove the internal balls.. replace with the bag and fill with pearlite. To above the clay level.. remove the waste bin..

It does seem to be working and it means i can just lift the bag out by the handles and start again.. :-)

Worms... I have no problem with them in my flooded beds - provided there is lots of air in all the different areas of the system

PH... I have lots of broken marble and limestone rocks around my system.. also I collect cast iron burners from old BBQs and drop them around to rust away.. I suppose it must help with Fe levels (naturally)..

I am planning another system, when I can tidy up that area, and want a similar hot tub... :-)
..
.

...
An alternative thought.. depending upon the contours etc... could you place some supports across the seats, leaving the well empty, and somewhere to stand your decorative interpretations ...

Ideally, I would sculpt something to tightly fit between "seat" areas, so the structure does not foul the general circulation... and... it can be lifted out for maintenance..

But do expect to have some fish hiding down there..
I think it is easily and practically doable and would be totally unobvious..
.
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