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Hi David,
You've got a number of options that might resolve your situation. The shadehouse would certainly help and the continuous access to water that is a feature of most aquaponic growing system, would also assist. Wicking beds are another option (that provides for continuous access to water) for growing vegetables and other plants using the water from your Koi pond.It's so hot here in North Texas that keeping my container and garden veggies from drying out is a problem. Since learning about AP, I’m thinking about using my Koi Pond Filter effluent (after the settling chamber) to be the nutrient supply for an AP system with DIY 2ftX4ft GBs. I’m still learning and planning at present – making sure I understand the basics. Additionally, I’m also considering a hoop shade structure.
I'd be surprised if the heat was an issue with a shadehouse and ready access to water. We have similarly harsh climates in Australia and aquaponicists live in most of them.Construction: I will build GBs from lumber I already have and line them with left over pond liner. I've been thinking about 8 to 10 inch deep beds with 3/4 gravel with the option of clay media on the top 4 inches in some of them, and maybe a floating raft option for leafy veggies. (However, it’s too hot to grow salad veggies here in the summer, will growing in an AP system make summer growing possible?)
If you're not relying on your growing system for nitrification or aeration, then you can set your pumps up to suit your plants' needs.Cycles per hour: The easiest system that I can imagine is a Flood and Drain run by a small take off pump in my filter, constantly flowing the nutrient fluid into the GBs, and exiting by bell siphon (or other method) to return to the Koi Pond. Is there a rule of thumb for how many Flood/Drain cycles per hour? As hot as it is here, I have to consider evaporation and transpiration when figuring the total amount of flood/drain cycles I use. The Koi pond will not be affected by the volume of water cycled, as it’s filtration is very stable and mature.
Many aquaponicists use products like Seasol (in Australia) or Maxicrop (in the US) to ensure that any deficiencies in their fish water are addressed. Once a system matures, there's usually little to be added.......perhaps a bit of calcium and potassium.Nutrients: As pond water has the Nitrogen for growing veggies, where do the other nutrients come from to support flowering and fruiting in an AP system? Are there supplements like seaweed extract that will need to be added?
A pH of 7.8 is good for fish and nitrifying bacteria. Plants prefer something closer to 5.5 - 6.5. You can go for a compromise......say around 6.8 to 7.0.....which many people do. From the plant's perspective, some nutrients will be locked up at this pH.Ph question: my city water has a pH of 7.5 to 8.0. My fish are happy and the pond has been very stable at about 7.8. Yet I read of AP systems running with pH in the middle 6s. The bacteria in my filtration system would not be as effective working with such low numbers – I know that from a pH crash I had years ago, where I was able to rescue the system by buffering up with Baking Soda to get the pH back to 7+. However, the filter bacteria were set back and I ran high Ammonia and Nitrites for a while afterwards. I realize that there are nitrifying bacteria that will bio-convert at various pHs but I don’t want to upset my stable system. So, my question is, can I run an AP system with a pH that is more in line with what my fish (and filter bacteria) are used to?
Another possibility is that you can just take water from your Koi system and drop the pH to around 6.0 and use it water wicking beds or hydroponic growing systems. Depending on your choice of system, you don't even need to return the water to the Koi pond. With this option, there's no need to compromise......and there are other benefits to had as well.
Gary
