Many decking oils can help slow down algae growth, but they don't completely stop it. These oils work by sealing the wood, which reduces moisture and, therefore, algae growth. Some decking oils also help protect against UV damage, but they need to be reapplied according to the manufacturer’s instructions to ensure the decking stays protected.

You don't need to seal your deck after painting it because most exterior paints are waterproof and weather-resistant. While stealing is not necessary, it can add an additional layer of protection.

Painting a damaged pool deck is not recommended if the substrate is crumbling, cracking, spalling, or otherwise actively deteriorating. Continuing deterioration will result in the paint also delaminating or flaking off the damaged surface. Minor damage such as chips or hairline cracks that are not actively deteriorating can often be repaired enough to paint over. A damaged pool deck with a lot of cracking and deterioration should be replaced for best results.

Applying a sealer or topcoat after staining wood is highly recommended, though not always strictly required. A sealer protects the wood from moisture, UV rays, and weather-related issues, which is especially important for outdoor surfaces like decks and fences. It also enhances the stain's durability, prevents fading over time, and gives the wood a cleaner, more professional-looking finish. For some indoor applications, a sealer may not be necessary, depending on the type of stain used and the level of protection needed. It's always best to check the stain manufacturer's recommendations and consider the wood's intended use and exposure when deciding whether to apply a sealer.