Regular stripper.

For the solid stain, we would think about 4-5 gallons for the two coats. In the future, you will not need to fully strip to reapply. See this for tips...

That is oxidation/graying that he did not remove fully. It will come off. Use the Restore A Deck Cleaner and Brightener kits for prep as they are much...

@old-crow Nothing, it is just as good as the others. They are all breathable and that is key when your deck is close to the ground.

Okay. Make sure to clean and brighten for prep. Look at the Restore A Deck semi-transparent stain or th wTWP 1500 Series.

Is the wood new?

TWP 1500 is allowed on ME. Do you have mildew or mold issues in the area?

@invisiblefireworks No, there is no reason. The work is the same by just putting a solid stain where you would use the semi-solid and it would blen...

It is impossible to add a stain of less opacity over a solid opaque stain. There would be zero reasons as well. Either sand it 100% off or reapply ano...

Strip and brighten for prep using this: Stain with a water-based stain like the Restore A Deck or Defy Extreme.

You cannot apply a semi-gloss to a deck, it would peel if you do and make removal extremely difficult. See this about new wood as well:/p>

@billybgood Strip and Brighten.

@billybgood Yes, it will be uneven at this point. You should remove the Defy fully now to get it even. Strip and Brighten.

Post some pics for help.

1. No, not really. 2. Yes, clean and brighten.