Your existing fish tank can be converted into a fully functional aquaponics system — growing fresh herbs and vegetables right at home using the water you’re already maintaining for your fish.
Why Convert an Aquarium to Aquaponics?
Most aquarium owners already do the hard work of maintaining water quality, feeding fish, and managing a biological cycle — they just don’t harvest any food from it. Converting your aquarium to an aquaponics setup adds a productive layer to your existing hobby without fundamentally changing your fish-keeping routine.
The benefits are compelling: fresh herbs growing on top of your fish tank, reduced water change frequency (plants do much of the nutrient processing), a more stable biological system, and the satisfaction of connecting your fish to productive food growing.
What You Need to Convert an Aquarium to Aquaponics
The core components of an aquarium aquaponics conversion are simple and affordable:
- Existing aquarium — Any size works, though larger tanks (100L+) provide more stability and growing capacity
- Grow tray or planter — Sits on top of or beside the tank; sized to roughly 25–50% of the tank’s footprint
- Growing medium — Expanded clay pebbles (hydroton) are ideal; rinse thoroughly before use
- Small submersible pump — Pumps water from the tank up to the grow tray
- Tubing and fittings — Connects pump to grow tray; return water drains back to tank via gravity
- Net pots or seedling plugs — Hold plants in the growing medium
- Plants — Herbs and leafy greens work best; basil, lettuce, mint, chives, and watercress are excellent choices
Step-by-Step Aquarium Aquaponics Conversion
- Choose your grow tray design — A simple plastic storage tray or purpose-built aquaponics grow tray works well. It should sit above or beside the aquarium with a gravity drain back to the tank.
- Drill or fit a drain outlet — A bulkhead fitting at the bottom or side of the grow tray allows water to drain back to the fish tank. A standpipe inside the grow tray controls maximum water depth.
- Connect your pump — Place the submersible pump in the aquarium and run tubing to the grow tray inlet. Use a simple timer to flood the tray periodically (e.g., 15 minutes every hour), or run continuously with a drain standpipe at the desired water level.
- Add growing medium — Fill the grow tray with rinsed clay pebbles to a depth of approximately 10–15 cm.
- Plant seedlings — Transplant healthy seedlings or rooted cuttings into the growing medium. Net pots help support plants and allow easy harvest and replacement.
- Monitor and adjust — Check that water is draining properly and not backing up. Test water parameters weekly; a functioning aquarium already has beneficial bacteria, so the transition to aquaponics is usually smooth.
Best Plants for Aquarium Aquaponics
Small-scale aquarium systems suit herbs and compact leafy greens best:
- Basil — Fast-growing, aromatic, and highly productive; a perfect aquaponics herb
- Mint — Vigorous grower; harvest regularly to keep compact
- Chives and spring onions — Low-maintenance and continuously harvestable
- Lettuce and spinach — Productive leafy greens that thrive in small systems
- Watercress — Loves aquatic environments and grows vigorously in aquaponics
- Parsley and coriander — Useful kitchen herbs well-suited to small aquaponics setups
Tips for Success With Aquarium Aquaponics
- Don’t overstock fish — Your existing fish bioload should be sufficient; adding more fish increases ammonia production beyond what a small grow tray can process
- Use LED grow lights — Unless the tank is in a very bright location, supplement with a grow light for strong plant growth
- Avoid harsh aquarium chemicals — Many water conditioners and medications are plant-safe, but always check before adding anything to a system with plants
- Start with hardy plants — Basil, mint, and lettuce are forgiving; save more demanding plants for after you’ve got the system running smoothly
Frequently Asked Questions
Will converting my aquarium to aquaponics harm my fish?
No — done correctly, aquaponics improves water quality for your fish by having plants process excess nutrients. The main risk is if the grow tray floods the tank excessively or disrupts existing equipment. Test changes gradually and monitor water parameters closely in the first few weeks.
How many plants can I grow on a 200-litre aquarium?
A 200-litre tank can comfortably support a grow tray of approximately 50×40 cm, which holds 6–10 herb plants or a mix of herbs and small leafy greens. It’s a modest but genuinely productive system for kitchen herbs.
Do I need to change water as often once I have plants growing?
Most aquaponics growers find that water change frequency reduces significantly once plants are established and actively absorbing nutrients. Some well-balanced systems require very infrequent or no water changes beyond topping up for evaporation.
Can I use saltwater (marine) aquariums for aquaponics?
Freshwater aquaponics is standard. Saltwater/marine setups are not suitable for most plants. Some specialised halophyte (salt-tolerant) plants can be grown with brackish water, but this is a niche and complex application not recommended for beginners.
What if my plants start to look yellow or unhealthy?
Yellowing is often a sign of nutrient deficiency — either because the fish bioload is too low for the plant demand, or because the system needs more time to fully cycle. Check pH (should be 6.8–7.2) and consider supplementing with a small amount of organic seaweed extract to boost micronutrients.
Ready to take your aquaponics beyond the aquarium? Get the complete build guide here and create a full-scale system in just 2 hours.