Now we are probably getting into some of the stuff Sylvia really wanted me to write about. In some places I'm known for my patience in re-explaining many of the basic info needed for stable home aquaponics system design.
Things like the three major functions of media filled flood and drain grow beds (actually there are more than three functions.)
1-Media filled flood and drain grow beds provide Bio-filtration
2-Media filled flood and drain grow beds provide solids filtration
3-Media filled flood and drain grow beds provide plant support and space for growing
Now we get into the additional functions that many people might forget about.
A-Flood and drain media filled grow beds do all of the above functions without needed any additional aeration added to the system
B-Flood and drain media filled grow beds provide a great home for composting worms.
C-Flood and drain media filled grow beds provide for mineralization of solids.
D-Flood and drain media filled grow beds don't require net pots or separate seed starting facilities.
E-Leaves don't foul up outdoor flood and drain media beds
F-Algae isn't a problem in flood and drain media beds
G-Flood and drain media filled grow beds give you a place to set down your drink as you use extravagant hand gestures to explain some point during an Aquaponic gathering or system tour.
Perhaps there are other points in favor of flood and drain media filled grow beds but there are a few points on the negative side.
-Flood and drain media beds can have a huge impact on temperatures, they make very good chillers on cold nights and they are great water heaters on hot summer afternoons. (constant flood during these times might be appropriate.)
-Gravel is heavy and a pain in the back to wash/haul.
-Lighter manufactured materials are costly and still need rinsing.
-Flood and drain causes water level fluctuation or requires a sump tank or sequencing valves.
-timed pumping can be hard on pumps
-variation in sounds from pumps turning on/off or siphons kicking in/out draw attention to the noise (constant sound fades to the background most of the time.)
Still, I like the gravel beds for their ease of use once installed. If a system is properly designed (has enough grow bed to handle the fish load) the gravel beds provide for a very low maintenance system able to be left to fend for it's own for a few days. This is important as I travel often and need something easy for the neighbor to check on. If you are going to do NFT or Raft(DWC) systems, you will need separate ways to deal with solids filtration and bio-filtration. With media beds, they take care of solids, bio, and plant space all in one.
Next primary bit of information people often need for designing their home system. How much filtration is needed for some given amount of fish. Here is the rule of thumb I learned.
3 kg of fish in 50 liters of water with 100 liters of grow bed or 6 kg of fish per 100 liters of fish tank with 200 liters of grow bed. THAT IS THE MAX!!!!! Ok so for my poor brain I rounded that out to an easy imperial measure to remember. 1 lb of fish per 5 gallons of gravel (again that is MAX!) Now keeping in mind that you can't really flood 100 liters of grow bed from a 50 liter fish tank and expect your 3 kg of fish to still be happy. To run this 2:1 ratio, you must have some method of dealing with water level fluctuations. That method traditionally was a sump tank, now there are more options with things like indexing valves.
Instead of using the above numbers, I now usually recommend something more like 20-25 fish per 500 liters of grow bed (assuming fish only being grown out to 500 grams) or 1 fish per cubic foot of grow bed media assuming 1 lb grow out of fish (1 cubic foot is around 7.5 gallons.)
Now I would never recommend some one try to grow a 1 lb fish in only 2.5 or even 5 gallons of fish tank. I've read a few places that say you can grow an eating size fish in something as small as 50 gallons, well perhaps you can with a fish as forgiving as tilapia but I like larger tanks. Very small fingerlings are fine in small tanks and I currently have over 100 small catfish in a 100 gallon tank but for grow out of large fish like catfish, my personal minimum size tank would be 300 gallons. I like a 600 gallon tank to grow out really big catfish. 300 gallons is also a good size to have more temperature stability.
Pumping now this is more important that many people think. How big a pump do I need for my system? Well the simple rule here is you should aim to pump the volume of your fish tank each hour. So if you have a 300 gallon fish tank and your design will have the pump run constantly, then you need your pump to move 300 gallons per hour at whatever height you will be asking of it. (A pump with a nominal rating of 300 will probably not move 300 gallons per hour once you hook it to plumbing and expect it to lift that water two feet above the surface of the fish tank.) Most good pumps should have published curves or information that will tell you aprox how much water it will move at different head heights. Now if you are going to be doing timed pumping, you need your pump to move at least the volume of your fish tank during whatever portion of an hour you will have your pump on. So if you plan to run 15 minutes each hour, then you should get a pump that will move 4 times the volume of your fish tank at the needed head height each hour. Then when you run it for 15 minutes, you will get the circulation you need. It is always wise to allow extra flow a bit beyond what you think you will need.
Plumbing and pipe sizes. Oooooh this is a stinger
So many people start their first systems with too small of pipe and find out later they should have used larger. Yea, the bigger pipe and fittings costs more but buying both the smaller stuff and a set of the larger stuff costs even more yet. Please remember that in Aquaponics there is this stuff we call bio-slime that can clog small piping. Algae can clog piping as well. For larger pumps, I'll connect the pump according to the pipe fittings the pump comes it. for small pumps, I now adapt up to larger pipe and I've found that a little tiny pump can sometimes actually move much more water than I expected. Even my ten gallon aquarium with a 20 watt pump is adapted up to 1" and 3/4" pipe.
Gravity drain plumbing, MAKE IT BIG!!!
Example, My big system, the pump uses 1 1/2" pipe, about half of the flow from the pump is being sent to the fish tank (probably 30 gallons a minute) the SLO (solids lifting overflow) drain from the fish tank is 3" sewer pipe. If I were to send all 60 gallons per minute from my pump to the fish tank, it would overflow even with the 3" drain. I know it is a real bummer cause the really large fittings get costly but so would overflowing the system and burning up the pump when the sump runs dry. Some people will use two 2" fittings instead which can work but keep in mind that the more pipe walls you are dealing with the more resistance. In other words, two 2" pipes does not equal one 4" pipe. A pump pushing water through a 1/2" pipe can still over top a 1" overflow. And then remember that the overflow will probably have grills or mesh over it and that can clog too (on to a next important point.)
Fish will swim through pipe.
I've had a 2 inch fish swim through 3/4" piping with six elbows! I've had tilapia fry make it through a gravel bed to get into the sump tank where they rode through the pump to get into a different fish tank!!!! And one of them survived!! But you can't expect them all to survive or even expect any of them to survive. Most fish find that sunning them selves on the surface of a grow bed to be very bad for their health. However, finding the fish on the grow bed is a little more pleasant than discovering one in a ball valve, or more accurately part of one in the ball valve "I wondered why that was so hard to close!" I've found that most fish find NOT swimming after eating to be very dangerous. I guess this will bring us to the next topic, tank covers. Most of the fish I find out of the tank get eaten by something else, like my chickens.
Fish tanks should have covers.
1-Fish tank covers keep fish in. Any fish tank that doesn't have a huge amount of extra depth above the water line risks fish jumping out.
2-Fish tank covers keep debris out. In outdoor systems things like leaves can really clog up the works. Even with a tank cover some leaves are gonna get in but a cover will keep huge amounts of plant matter out of your fish tank and also the screens, grates, pumps, traps and plumbing.
3-Light. Shade the tank to keep excess sunlight out and avoid a major algae bloom. Pea soup can really mess with dissolved oxygen levels even to the point of killing fish. String algae can just gunk things up and create more work in pump/screen cleaning. A cover over the tank will keep light out or at least make it easy to throw extra fabric, shade cloth or a tarp over to block the light and stop the algae.
4-children and pets. Kids love to play in water but if you have children around, make sure your tank cover will keep them out unless supervised. I also recommend covers if you have ducks around or dogs/cats that might manage to get into trouble while trying to sneak a snack.
6-Since my property isn't fenced, I've also added a lock to the cover on my large tank. Yea I know it will only keep honest people honest.
Galvanized tanks, Don't do it!!!!!!
Metals!!!!!!!!!! They are generally not appropriate for aquaponics.
Many metals can quickly corrode in aquaponics. They can build up to toxic levels for fish in a recirculating system. Of particular importance to note are copper and zinc. Both can be particularly detrimental to some types of marine life. Galvanized tanks can leach zinc into water and it becomes more problematic the lower the pH. Copper plumbing can leach too. In our household plumbing this in not normally a problem as the water is only taking the single trip through the plumbing but in an aquaponics system the water circulates through the parts constantly and aquaponics also sometimes tends to the acidic side which can speed the process. Hence a copper coil would not be a good idea for a water heater for aquaponics. There are other metals that can be an issue (perhaps nickle from chipped bathtubs) but copper and zinc are the two that cause the most issues in Aquaponics in my reading.
Look for something that won't affect your pH. This rules out limestone and marble since they will cause a really high pH. Also, I don't recommend shells, my system is full of them and my pH stays at 7.6 unless I'm really overloading it. I've heard that Diatomite will lower pH but one might want to be careful if growing trout in such a system since it apparently also has levels of zinc that might be bad for trout at the lower pH. I like river rock of 1/2" size. Lava rock can also be good if you can get it in the right size range but it is really difficult to get washed very clean. Clay balls are great if you can afford them and your back can't afford the lifting of gravel. I recommend using small buckets and baskets for the washing. I can do the washing so long as I don't lift too much at any one time. Set up the washing station so you don't have to bend over too much and it can be done without injury.
Plumbing a bypass
Don't restrict your pump. If your pump gives more flow than you can handle, then use a bypass. Simply a T back into the same tank where the pump is located. Put the ball valve on that flow and adjust the ball valve till the flows are balanced as needed.
I think I'm about out of steam on this post. All these things I've repeated many times on forums to help out people struggling in one way or another with their physical system designs. I hope these things help more people on their journey into Aquaponics.