Backyard Aquaponics
A place to discuss aquaponics

Just a quick question.

How long will a grow bed continue to sustain plants now that I have no fish in the system, and more importantly how long will the bacteria survive? I have all the pumps running as they were and I have used seasol and worm castings into grow bed. been empty about two weeks now

Thank you

Hi Ozzy, i ran my AP system over summer with no fish supplementing with Charlie Carp. I think i'll try Seasol Powerfeed (for the nitrogen) this time around as the CC was rather stinky and, although plants, grew they didn't really thrive.

As this is the second year of my AP system the solid waste load in the GB's hopefully is now good to carry plants across the no-fish period but i'll keep an eye and use powerfeed this time around if necessary.

If you're supplementing the plants will go on just as if the fish were in the system. If you're not supplementing then it depends on the age of the system, the nutrient reservoir left in the system and the number and type of plants you're growing.

Don't be too concerned about the bacteria they'll survive a long time even without feeding, their numbers might be reduced but any organism deaths will provide food for those that survive. I've had them last 6 months on moist media stored in bags and when added to a new system there was no cycling time so they're pretty durable.

As noted above "it depends" without an ammonia source the bacteria will decline but if you supplement some ammonia source you can keep the bacteria colony strong for when you plan to add fish again. The bacteria won't die out completely but if you leave the system without fish and no ammonia source for a long time you may need to "cycle up" again when you do add fish. If you leave it without a nitrogen source for too long your plants will start to get a bit yellow starting with the older leaves first if they are suffering from nitrogen deficiency.

If the system was very mature and had a heavy load for a long time and has "banked" a lot of nutrients in the solids that are slowly mineralizing in the grow beds, you may be able to go quite a long time before seeing a decline in the plants but that will also depend on how greedy the plants you are growing are, some use up nutrients faster than others.

Myself, I've basically been running "hydroponics with some fish in the tank" for some time now since I grow a huge amount of veggies but I don't have a market for the fish so we have been reducing the stock of fish. So I have to do extensive water testing so that I can mix up fish safe hydroponic nutrients to supplement my system with since I don't have enough fish load to feed the plants.

Hi Ozzy
I am back in the Forum after a long break.
2 years ago I stopped using fish as the food source, too many temperature problems with trout, stinking water with silver perch, so I emptied the tank, refilled with fresh tankwater and added worm juice and castings from the worm farm.
2 years total success, summer tomatoes and greens, winter broccoli and celery. All fed with worm farm juice every 2 weeks or so, , plus an occasional top up with Charlie Carp and Seasol.
Now I can go on holidays with no fish feeding problems, the cat is regretting the jumping trout syndrome and we have fresh veg all year. I also grow duckweed in the tank to feed my goldfish (seperate ornamental pond), and when that dies, it adds to the nutrient base. Win Win.

Yep, it's not the fish themselves that provide the nutrients but what is fed to them so if you can figure out how to feed the system, you don't necessarily have to do it by way of fish. (Though I suppose it isn't technically aquaponics if you don't have fish in there.)

Hydroponics