I'm a long time fishkeeper, from goldfish to stony coral based reef systems. I really like your setup, awesome use of natural systems
Some things I would keep in mind. I would not add any gardening nutrient mixes to the tank. The end product of the nitrogen cycle in your tank is nitrate, which is a readily accessible form of nitrogen that your plants will thrive on. This is the result of ammonia being broken down by bacteria, and that bacteria needs space to grow. Make sure you have lots of submerged surface area (might even look into fluidized bed filters, they are awesome, and provide more surface area per volume that pretty much anything) and good gas exchange. Gas exchange in water is directly proportional to the temperature of the water (cooler water holds more oxygen), and the amount of surface area exposed to air. Things like bubblers are great for providing movement, but actually are not a great source of surface area (they actually provide way more gas exchange by sending ripple over the surface when they break than they do rising through the water, but pumps agitating the surface are WAY more efficient). The vast majority of your surface area is at the top of the tank, and the more surface agitation you can provide, the more gas exchange will happen (up to the saturation point for that temp). The ammonia that breaks down into nitrate is provided by fish waste, so personally I would make sure you have a beefy filter and good surface area and then overstock it. Feed liberally. Fish like goldfish and mollies and the like are ideal (though goldfish like cooler water, and I'm not really sure what temp you want the water for your plants). A high stocking level will also have the added benefit of producing a lot more co2, just make sure you have good gas exchange. Frequently gravel vac the tank, decanter the detritus, and it makes very good fertilizer. There are also many micr-nut's which you can get specifically for aquarium use (many of them are must haves for reef systems, just make sure they don't have salts in them). That is what I would recommend using to dose anything that isn't already in your water. Most fish food is also very high in phosphates, just make sure you don't rinse it first.
Some things I would keep in mind. I would not add any gardening nutrient mixes to the tank. The end product of the nitrogen cycle in your tank is nitrate, which is a readily accessible form of nitrogen that your plants will thrive on. This is the result of ammonia being broken down by bacteria, and that bacteria needs space to grow. Make sure you have lots of submerged surface area (might even look into fluidized bed filters, they are awesome, and provide more surface area per volume that pretty much anything) and good gas exchange. Gas exchange in water is directly proportional to the temperature of the water (cooler water holds more oxygen), and the amount of surface area exposed to air. Things like bubblers are great for providing movement, but actually are not a great source of surface area (they actually provide way more gas exchange by sending ripple over the surface when they break than they do rising through the water, but pumps agitating the surface are WAY more efficient). The vast majority of your surface area is at the top of the tank, and the more surface agitation you can provide, the more gas exchange will happen (up to the saturation point for that temp). The ammonia that breaks down into nitrate is provided by fish waste, so personally I would make sure you have a beefy filter and good surface area and then overstock it. Feed liberally. Fish like goldfish and mollies and the like are ideal (though goldfish like cooler water, and I'm not really sure what temp you want the water for your plants). A high stocking level will also have the added benefit of producing a lot more co2, just make sure you have good gas exchange. Frequently gravel vac the tank, decanter the detritus, and it makes very good fertilizer. There are also many micr-nut's which you can get specifically for aquarium use (many of them are must haves for reef systems, just make sure they don't have salts in them). That is what I would recommend using to dose anything that isn't already in your water. Most fish food is also very high in phosphates, just make sure you don't rinse it first.