If the black stains are from dog pee, pour hydrogen peroxide on the spot. It may bubble - that's OK. When it stops bubbling, dry the spot. You may have to do this a couple times until it stops lightening the area. If all else fails, sand and restain the area.
The dark stains on the floor arecaused by a reaction between the urine, basically ammonia and the tannins in the wood. Using an oxidizer such as hydrogen peroxide or an oxygen based cleaner may help diminish the dark stains.
Every time I clean my mirrors, they end up having tons of streaks and almost look worse than before I started. What could I use to clean them that won't leave streaks...
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Here is a post with similar question and some positive replies.
https://www.hometalk.com/diy/clean/house/q-how-to-get-dog-pee-stains-out-of-hardwood-floors-31276933
How to get dog pee stains out of hardwood floors.
If the black stains are from dog pee, pour hydrogen peroxide on the spot. It may bubble - that's OK. When it stops bubbling, dry the spot. You may have to do this a couple times until it stops lightening the area. If all else fails, sand and restain the area.
The dark stains on the floor arecaused by a reaction between the urine, basically ammonia and the tannins in the wood. Using an oxidizer such as hydrogen peroxide or an oxygen based cleaner may help diminish the dark stains.