Do live plants affect the nitrogen cycle?

Switching from plastic to live plants is one of the best upgrades you can make — and yes, live plants absolutely interact with the nitrogen cycle, mostly in your favour. Plants consume ammonia and nitrate directly as nutrients, which means a well-planted tank cycles faster, runs cleaner, and stays more stable than a bare or plastic-planted one. They won't replace your filter bacteria, but they work alongside it. To give you the right advice on where to start, what size is your tank, how long has it been running, and what fish are you keeping in it?

Perfect setup for live plants — an established 120 litre community tank is exactly where they thrive. Good news on the cycle side: because your tank is already mature, you've got a solid colony of beneficial bacteria in your filter media. Adding plants won't disrupt that. What actually happens is the plants start pulling ammonia and nitrate directly, so you may find your nitrate readings drop noticeably within a few weeks. That's a good thing. What lighting have you got on the tank at the moment — is it the original hood light, or have you upgraded it?

That's the one thing worth being honest about — most stock hood lights are low output, which limits you to low-light plants. The good news is that low-light species like Java fern, Anubias, and Cryptocoryne are brilliant for community tanks, nearly indestructible, and your corydoras will love the cover. The thing those plants do need, even in low light, is a good liquid fertiliser. Substrate nutrients get used up faster than people expect, and without supplementing, plants go yellow and decline within a month or two. I'd recommend Tropica Plant Growth Fertiliser — it's the standard that serious planted tank keepers use, dosed weekly, covers all the micro and macronutrients, and it's very well suited to low-tech community tanks where you're not injecting CO2. A 300ml bottle lasts a long time at the recommended dose.

Not at normal doses, no. Tropica's formula is designed for fish-safe use — the nutrients go straight to the plants rather than sitting free in the water column long enough to cause problems. The one thing to watch is phosphate if you're ever dealing with algae, but in a stocked community tank with regular water changes, that's rarely an issue. Dose as directed on the bottle — usually 5ml per 50 litres once a week — and you'll be in good shape. Your tetras, corydoras and gouramis will actually benefit from the improved water quality the plants bring as they get established.

Do it gradually if you can. Swap out a few plastic plants at a time over a couple of weeks, replacing each one with a live equivalent. It gives the new plants time to root and establish before you add more, and it keeps the tank looking full throughout. Start with the easiest spots — Anubias tied to any wood or rock you have, Java fern attached the same way, and Crypts planted into the substrate. None of those need high light and all three will be happy under your hood. Once you're happy with how it's going, you can always reassess the lighting later if you want to expand your plant options.