The answer to this is relatively straightforward and there are two ways to go. First, if you have a small coating of mould, algae or mildew on your tile grout then you could use a simple tile cleaning product like Shower Tile Cleaner. This should more than do the job for you.
However, if you have a thicker coating of mildew, algae or mould on your tile grout then we’d suggest spraying some diluted household bleach onto the stained areas and leave the bleach on there for at least an hour – always test on a small area first to be safe. Then, rinse it off well using plenty of clean water. This will certainly clean off all the mould for you. If you still have stains left remaining then perhaps you should consider recoloring the grout with Grout Colorant.
Copyright Ian Taylor and The Tile and Stone Blog.co.uk, 2013. See copyright notice above.
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It will really help me a lot.