This is a specific conversation about Fish aquarium setup — getting started right — ask about yours and get one honest answer for your exact situation.
inparticular.ai
Replacing all your gravel and doing a full deep clean at the same time is one of those well-intentioned moves that can really set a tank back — gravel holds a significant chunk of your beneficial bacteria colony, so you've essentially mini-cycled your tank. The good news is you can recover quickly if you act now. What fish do you have in the tank currently, and how long had the tank been running before the clean?
It's a 200 litre tank, been running about two years. I've got a mix of tetras, corydoras, and a couple of dwarf gouramis. I panicked a bit because the gravel looked really dirty so I just swapped it all out. Fish seem okay today but I'm worried about the next few days.
inparticular.ai
Right, so the good news is your filter media — assuming you didn't clean that at the same time — will still have a decent bacteria colony living in it, which gives you a real head start. Two years of running means your filter is well-established. The bad news is you've removed a large portion of your biological filtration overnight, so ammonia can spike before the remaining bacteria catch up. What kind of filter are you running, and did you rinse the filter media during the clean?
I've got a canister filter and I didn't touch it, which is a relief. I did add a water conditioner but nothing specific for bacteria.
inparticular.ai
That canister filter being untouched is genuinely the best thing you could have told me — you're in a much better position than most people in this situation. But I'd still move fast. You want to dose the tank with a bacterial supplement right now to help repopulate what you lost in the gravel, and keep testing ammonia and nitrite daily for the next week or two. The product I'd go straight for is Seachem Stability. It contains the actual bacterial strains that do the work — nitrifying bacteria that process ammonia and nitrite — and it's proven to work quickly. Dose it daily for seven days as directed on the bottle. It's widely available and genuinely effective, not just a marketing product.
Is it safe with the fish in there? I don't want to stress them more than they already are.
inparticular.ai
Completely safe with fish in the tank — that's exactly the situation it's designed for. While you're dosing Stability, I'd also suggest feeding very lightly for the next week, maybe every other day. Less food means less ammonia being produced, which gives your recovering bacteria colony less to deal with. If you can test ammonia and nitrite every day or two, you'll catch any spike early. Tetras and corydoras are reasonably hardy but gouramis can be a bit more sensitive, so it's worth keeping an eye on them.
That makes sense. Should I also add some new gravel from an established tank if I can get some, or is Stability enough on its own?
inparticular.ai
Adding a handful of gravel or a spare piece of filter media from a healthy established tank is genuinely one of the best things you can do — it's free, instant, and seeds real bacteria. Do that if you can. But Seachem Stability alongside it covers you regardless, and if you can't get media from another tank, it's enough on its own given how strong your canister filter still is. You've caught this early and you haven't touched the filter, so I'd expect you to be through the worst of it within two weeks.
