Diary - I was startled by how my dad has been washing his face.

[Maybo]

This is an entry from my diary. Please check it and correct any mistakes.

I was startled by how my dad has been washing his face. He has been using bar soap to rub his face directly. That was the reason he got an infection on his eyes a couple of weeks ago. The bar soap must have been contaminated. He also has toothache quite often. My mum once told him to change a new toothbrush because his toothbrush had turned black, but he refused and insisted to use the old one. He also blamed mum for blackening his toothbrush using bleach. Nobody has done that!

 

[emsr2d2]

I was startled by surprised to discover how that my dad has been washing his face no full stop here He has been using bar soap to by rubbing a soap bar directly onto his face. directly.

This didn't need to be two sentences.

That was the reason That's why he got an eye infection on his eyes a couple of weeks ago.

See above. Use the simpler "eye infection". If for some reason you really need to use your word order, use "in his eyes".
How do you know that's what caused the infection?

The bar of soap must have been contaminated.

This is vague. What is it meant to have been contaminated with?

He Also, he has gets toothache quite often.

Note my preferred word order above.

My mum once told him to change get/use/buy a new toothbrush because his toothbrush had turned black, but he refused and insisted to use on using the old one.

See above. Note the correct construction "insist + on + verb-ing".

He also blamed Mum for blackening his toothbrush using bleach.

Does he not understand what bleach does? If you'd used "my" before "mum", the uncapitalised form would have been correct. However, as written, you're using "Mum" as a title so it should be capitalised.

Nobody has done that!

Do you mean "No one in the house damaged his toothbrush" or "No one in the world has ever damaged a toothbrush with bleach"?

 

[Tarheel]

This is an entry from my diary. Please check it and correct any mistakes.

I was SURPRISED ABOUT how my dad has been washing his face. He has been using bar soap to rub his face directly. That was the reason he got an infection on his eyes a couple of weeks ago. The bar soap must have been contaminated. He also has toothacheS quite often. My mum once told him to change TO a new toothbrush because his toothbrush had turned black, but he refused and insisted ON USING the old one. He also blamed mum for blackening his toothbrush using bleach. Nobody DID that!

What you could do is throw the old one away and replace it with a new one when he's not looking.

 

[Maybo]

How do you know that's what caused the infection?

This is vague. What is it meant to have been contaminated with?

There were black spots on his soap. Very dirty.

Does he not understand what bleach does?

He didn’t believe that bleach can’t blacken things until Mum bleached a toothbrush in front of him.

"No one in the house damaged his toothbrush"

I mean that. No one in the house has ever damaged a toothbrush with bleach.

 

[Maybo]

What you could do is throw the old one away and replace it with a new one when he's not looking.

He picked it up from the rubbish bin and used it again. We finally managed to throw it away.