That is internal discoloration of your wood type. Cleaners will not remove it. Brighteners may help but hard to say for certain. I doubt sanding will ...

Yes, you can do this.

It could be due to the gloss sealer. They gave you bad advice.

You cannot use a gloss sealer on a wood deck. It will peel, blister, and attract mildew. You will need to remove it fully. Most likely by sanding. Onc...

Post pictures.

No, it is not the origianl good stuff and they changed all their formulas when they sold the company to Zinser. None of it is the same as it used to b...

We would never use the Cabot based on changes in formulas recently. Try a better brand as the products are not the same anymore. See here for new w...

Strip and brighten for prep with Restore A Deck Kits: It does not harm Trex. Try a better brand of stain than Penofin or Cabot:

"Modified oil" means it is still water-based.

We would honestly not use either one of those brands as they heave a tendency to peel and look opaque when custom mixed. No custom blended semi-transp...

You will need a solid stain to get it to all blend. Strip and brighten the wood for prep.

You can use it on Mahogany wood. We like the TWP Rustic 1516 color for it.

We have used both and would not suggest them. Of the two, the Sikkens is better though. No other Clear products will give any UV protection and honest...

You will need to sand it all off to be able to use any other product. If you cannot, then you may need to replace the boards.

No, whenever switching brands you should remove the previous coating. Water-based stains do dry faster so you should work a little quicker.