Yes totally doable and can even be less work than that. Just buy a planter that can sit on top of your tank (should be fine) then fill with hydroponic clay balls. To double as a filter just get some eggcrate and block off some of it and put some sponge in/whatever other filter media you want. then drill in some bulkheads one that enters about at what the desired water level is (output side), then at the bottom or pumping right to the top above the water level for the input throw a pump in the aquarium towards the bottom on the opposite side of the output and youre gold. Ive seen some videos of this online its pretty cheap doable and a great way to keep nitrates in control.

Here is one video by Joey that has the basic construction just need to tweak it a bit for the herbs, the clay balls work like ceramics for bio FYI:
https://www.youtube.com/watch?v=YFcioRUCa6c&list=PLcWeEm9w62maaz5-CO-M0O7MzldTzRRhn&index=2

Bump: Also some things can just grow in a HoB filter sponge (pothos is commonly added that way for nitrates)

 

I'm planning to try growing rosemary in a shower caddy resting on the spray bar of my goldfish tank. I use clay balls and sphagnum moss in the riparium plants I already have there.

 

Be careful with the sphagnum moss it will make the pH more acidic which could be harmful.

 

The moss is not in the actual tank water, just dipped and stays moist for the roots. There's only a very small amount of moss in there anyway. Only a little bit of the clay balls are actually under the water line. I have city water that has no buffering capacity and the ph used to drop before I started running crushed coral in my filter. Now I keep my goldfish at a pretty steady 7.4, so no issues with the moss and ph.

 

Check the threads in my signature for ideas. The riparium build thread has ideas and my 25g build thread has a riparium on it that sounds very similar to what you're looking at building

 

Basil and cilantro- yeah. Rosemary can grow into a small shrub, maybe you don't want that one in an HOB container. And mint will take over and crowd everything out- put that one in its own container and trim it aggressively. (This is coming from my experience growing herbs outside- I never grew them on a tank)

 

Yea, I know how the herbs act in nature. Just saying what I'd like to have. Mint is an effing WEED, and rosemary is a tree.

 

I had a similar filter about a decade ago on a turtle tank with a window planter box. I put a couple of 3/4" barbed bulkheads at one end, partitioned them off with egg crate, then filled the rest with lava rock. Put a powerhead in the tank plumbed to a U shaped bit of PVC (similar to a canister filter return) and stuck it in the opposite end of the box from the drain. Stuck the box on a pass thru between my dining room and living room and grew pothos in it. They grew like crazy in that nasty turtle water.

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Just a tip: rosemary does better in dry conditions seeing as it's from the Mediterranean area. In my experience, it usually rots when constantly kept in water - even if the water is moving.

Mint I'd a great choice because it's usually found near wet areas - near Forest streams, ditches, and wet Meadows. The basil and cilantro are good candidates, as are parsley, chives (tricky but it can be done), and a few others.

If you're open to veggies, there's a LOT that you can do - lettuce, tomatoes, beans, peas, and peppers are the ones that come to mind for aquaponics.

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Yea, I just want to keep it small for now, seeing as I am running a 30 gallon tank and am in an apt.

 

My 29 gallon from many years back had a giant emmersed Oakleaf Water Sprite that was a good foot and a half in diameter or more of aerial leaves growing out of my HOB. It actually became a good part of the old AquaClear sponges I used on that massive old filter. It was growing right under a 125 watt Mercury Vapor lamp and was getting blasted with light.

 

Pennyroyal is a marginal flooded meadow plant and loves moisture, good for repelling Cat and Dog's fleas. I seem to recall that Catnip is also good with damp soil. I grow lots of Chives and it's fine with damp as long as the roots are fed with fresh and it's properly draining and not pooling around their root crowns.

The Riparium section of General Aquarium Forum here has an article or three about using HOB's, breeding boxes and refugeariums as emmersed root planters.

 

I've been giving this a bit of grey matter real estate, and I think for this to be feasible, I'm going to have to sump my tank. That way I don't have a fluctuating water volume in my main display....

 

To get any good flavor or growth out of herbs, they need medium-to-high light conditions (except maybe mint, chives or parsley). (I mean high light for air-grown plants, which is much higher than that used in aquariums, for the most part). I would be worried about all that waste light hitting the aquarium and causing algal blooms, so you would want to plan around that.

Most herbs prefer a lower pH than the average tank when grown hydroponically: (ph/ TDS/PPM Levels for Herbs) It may be difficult to get them to thrive outside their ideal range. I haven't tried growing any herbs hydroponically above pH of 6.5 (and never with aquarium in the same loop) so I have no idea which would be the best candidates, besides mint, which can survive anything.

Also, cilantro is an annual, so it will try to bolt and flower after a couple of months (the good news is that the seeds are a spice [coriander] and that the root is is usable for southeast Asian cooking). Just make sure your set up allows you to pull plants easily, if you grow it, as after it sets seed it will die.