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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.

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?)

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.

Nutrients: As pond water has the “N” for growing veggies, where do the “P” and “K” come from to support flowering and fruiting in an AP system? Are there supplements like seaweed extract that will need to be added?

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?

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Perhaps I'll answer you in reverse order here.
pH, my big system runs a pH that rarely drops below 7.6 because I made the mistake of using shells as 40% of my media and they buffer to about 7.6. I still manage to grow stuff though I would probably have less issues with Iron deficiency if I had a lower pH. You can keep your pH where it works well but you may need to regularly supplement with chelated Iron to make the plants happy and some plants may never thrive in the system while others will do better. (I've never had much success with cucumbers or strawberries in my high pH system and I would not even attempt blueberries.)

Nutrients. We know the N is there is we test for that. I think you would find that if you tested the P, it would be there too. Fish feed and fish poo tend to provide those well enough. Sometimes the potassium needs to be supplemented and this is usually where the seaweed extract comes in. Sea salt sometimes can help with this too. But depending on your fish feed, some people don't even need to supplement that either.

Cycles per hour, well that all depends on how you set things up. Some people will use a pump on a timer and a slow drain back to the fish tank. Others will run the pump constant and let an auto siphon deal with draining. Which you use will depend on the layout of the set up and what you want to tinker with. If you don't have much fall from the grow beds to the pond the siphons might be tricky. It can also depend on the type of pump available for the purpose. If it's a small pump that you want to run continuously, then the siphons are the way to go. If it's a larger pump that you only want to run say 1/4 th of the time, the a timer is probably a better choice. Floating raft would not get a siphons and usually should have a constant small flow plus some aeration but you are right about not all crops being well suited to floating rafts (though you can grow a larger variety in a raft than you might think, it just means you can't go lifting the whole raft out for harvest if you have vines growing up a trellis on one end.) You can grow herbs, vines, flowers and other things in rafts but some root crops won't be well suited to rafts and heavy plants would tend to sink some rafts or even grow too big for the holes/pots. So what method you choose should be based somewhat on what you will be growing and how you want it to look. Gravel beds can be quite ornamental while a raft is going to look a bit sad when plants are tiny or when you have harvested a bunch of it.

I will warn against lumber and liner in termite territory. I've been replacing all my lumber and liner grow beds over the past year. Liner is ok so long as it isn't near wood. Termites chewed right from the wood into my liner and I had leaks. Granted, my lumber wasn't pressure treated but even if it had been, that only slows the termites, doesn't necessarily stop them.

If you can, make the beds deeper, especially for the gravel bed if you do go with a siphon, I really recommend 12 inches deep as a great functional minimum, I know it can be done shallower, I've done it but I now really love extra deep beds (most of my gravel grow beds are now 24 inches deep.)
Thanks for the detailed reply TC, I appreciate your input.

I plan on using a small pump for continuous flow which I can adjust to determine the flood time. The drain time will be dictated by the size of the bell siphon and it's related discharge plumbing.

How many flood drain cycles should I aim for - once every 5 minutes, 10 minutes, 15 minutes? I read where one person was using one cycle per hour. I think Murray was cycling every 12 minutes - is that a good place to start?


TCLynx said:
Perhaps I'll answer you in reverse order here.
pH, my big system runs a pH that rarely drops below 7.6 because I made the mistake of using shells as 40% of my media and they buffer to about 7.6. I still manage to grow stuff though I would probably have less issues with Iron deficiency if I had a lower pH. You can keep your pH where it works well but you may need to regularly supplement with chelated Iron to make the plants happy and some plants may never thrive in the system while others will do better. (I've never had much success with cucumbers or strawberries in my high pH system and I would not even attempt blueberries.)

Nutrients. We know the N is there is we test for that. I think you would find that if you tested the P, it would be there too. Fish feed and fish poo tend to provide those well enough. Sometimes the potassium needs to be supplemented and this is usually where the seaweed extract comes in. Sea salt sometimes can help with this too. But depending on your fish feed, some people don't even need to supplement that either.

Cycles per hour, well that all depends on how you set things up. Some people will use a pump on a timer and a slow drain back to the fish tank. Others will run the pump constant and let an auto siphon deal with draining. Which you use will depend on the layout of the set up and what you want to tinker with. If you don't have much fall from the grow beds to the pond the siphons might be tricky. It can also depend on the type of pump available for the purpose. If it's a small pump that you want to run continuously, then the siphons are the way to go. If it's a larger pump that you only want to run say 1/4 th of the time, the a timer is probably a better choice. Floating raft would not get a siphons and usually should have a constant small flow plus some aeration but you are right about not all crops being well suited to floating rafts (though you can grow a larger variety in a raft than you might think, it just means you can't go lifting the whole raft out for harvest if you have vines growing up a trellis on one end.) You can grow herbs, vines, flowers and other things in rafts but some root crops won't be well suited to rafts and heavy plants would tend to sink some rafts or even grow too big for the holes/pots. So what method you choose should be based somewhat on what you will be growing and how you want it to look. Gravel beds can be quite ornamental while a raft is going to look a bit sad when plants are tiny or when you have harvested a bunch of it.

I will warn against lumber and liner in termite territory. I've been replacing all my lumber and liner grow beds over the past year. Liner is ok so long as it isn't near wood. Termites chewed right from the wood into my liner and I had leaks. Granted, my lumber wasn't pressure treated but even if it had been, that only slows the termites, doesn't necessarily stop them.

If you can, make the beds deeper, especially for the gravel bed if you do go with a siphon, I really recommend 12 inches deep as a great functional minimum, I know it can be done shallower, I've done it but I now really love extra deep beds (most of my gravel grow beds are now 24 inches deep.)
On the siphon you need to keep it's size in the relative functional range for the pump you are using. If you put in a tiny pump and a large bell siphon, the tiny pump will never kick it in fully and you end up with a constantly flooded bed that just trickles over the top of the siphon.

You probably already know this but it is usually pretty inefficient and bad for the pump to restrict the pump flow, it would be best to bypass excess pump flow back to the pond or somewhere else rather than simply restricting the flow.

As to what timing is best, hard to say. With timers, most people flood for 15 minutes and then leave the pump off for 45 but that can be altered depending on season and situation. Most of my flood and drain beds are getting flooded for 15 minutes and then they get between 30 minutes and an hour and a half to rest depending on what system they are part of.

With a siphon you will be filling again as soon as the siphon finishes so you will of course get more cycles per hour. How long it takes doesn't really matter so long as there is some flood and drain action and the water is moving since that is what aerates the water for the plants and bacteria.
Thanks again TC, yes, I do know about a pump output bypass to control flow and I understand about the fill rate necessary to trip the Bell Siphon. I'm planning on adjustable continuous flow initially and using the siphon to empty, and playing with those in/out parameters at first to get the flood/drain sequence to where I like it. I'm also interested in the FLOUT Siphon as a possible simpler, less fussy and more reliable emptying devise. (I'd like to talk to someone who uses one.) Until I have a working system, I want it to be KISS! Timers and more sophisticated sequencing will have to come when I have more experience.

TCLynx said:
On the siphon you need to keep it's size in the relative functional range for the pump you are using. If you put in a tiny pump and a large bell siphon, the tiny pump will never kick it in fully and you end up with a constantly flooded bed that just trickles over the top of the siphon.

You probably already know this but it is usually pretty inefficient and bad for the pump to restrict the pump flow, it would be best to bypass excess pump flow back to the pond or somewhere else rather than simply restricting the flow.

As to what timing is best, hard to say. With timers, most people flood for 15 minutes and then leave the pump off for 45 but that can be altered depending on season and situation. Most of my flood and drain beds are getting flooded for 15 minutes and then they get between 30 minutes and an hour and a half to rest depending on what system they are part of.

With a siphon you will be filling again as soon as the siphon finishes so you will of course get more cycles per hour. How long it takes doesn't really matter so long as there is some flood and drain action and the water is moving since that is what aerates the water for the plants and bacteria.
Truth is, most people think of timers as less tricky. But siphons can be great too. I've used a home made FLOUT before and once adjusted they are really good. (can be tricky to make and get working right but once they do they tend to be solid.)

The biggest problem with the FLOUT is they require a fair amount of space to operate either in the grow bed or in an external container. A bell siphon only takes up space right over the drain (which is generally not used for planting anyway) and a loop siphon can be external and not take up much space at all.

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