Cat stain bleach patch on dark carpet fix

That's a frustrating situation — hydrogen peroxide is genuinely useful on light carpets but it's an oxidising agent, so on dark fibres it strips colour almost immediately. The bleach patch is a separate problem from the odour, and unfortunately you can't undo that discolouration without professional carpet dyeing. But the good news is the smell is still very fixable. The only products that permanently eliminate cat urine odour are enzyme-based cleaners — they break down the uric acid crystals that cause the smell rather than masking it, which matters because if any odour remains your cat will keep returning to that exact spot. To point you to the right product: is the urine stain still visible, and would you say it's now set-in rather than fresh given you've already treated it once?

That ammonia smell means uric acid crystals are still active in the carpet fibres and probably in the underlay beneath. A week-old set-in cat stain needs a proper soak-through rather than a surface spray — the enzyme cleaner has to physically reach wherever the urine soaked to. Maine Coons are big cats, so the volume deposited tends to be larger than average, which means it likely penetrated deeper than you'd expect. Can you tell me roughly how large the affected area is, and does it have a carpet pad underneath?

Got it — 20cm with thick underlay means you need to apply generously and let it dwell. My recommendation is Simple Solution Extreme Pet Stain and Odour Remover. It's a professional-strength enzyme formula, widely available on Amazon UK, and it's specifically designed for set-in stains with a contact time that allows it to work down into underlay. Pour it directly onto the area until the carpet is saturated to the same depth the urine reached — don't just dampen the surface. Cover it with a damp cloth or cling film to stop it drying out too quickly, leave it for at least 30 minutes, then blot dry. Don't rub, and don't use any heat to dry it as that sets uric acid further. You may need two applications given how set-in it is. The bleach patch will remain visible, but once the odour is fully gone your cat will lose interest in the spot completely.

No — enzyme cleaners work through biological action, not chemical oxidation, so they won't bleach or strip colour from carpet fibres. That's exactly what makes them safe where hydrogen peroxide isn't. Simple Solution is colour-safe and won't expand the bleach patch. The only thing that will affect the appearance of the carpet going forward is heat or vigorous scrubbing, so once you've applied it, blot gently and let it air dry naturally. If the bleach patch is bothering you aesthetically once the odour is sorted, a carpet repair specialist can dye individual fibres back to the original shade — it's surprisingly affordable for a small patch.

Good — just make sure you're genuinely saturating the area rather than surface-treating it, that's the step most people skip and it's why the smell comes back. If after two applications you're still detecting odour, it usually means the underlay itself has absorbed the urine and may need to be lifted and treated or replaced. But try the thorough soak method first — for most set-in stains it does the job completely.