Coverage on VS721 is about 400 sq ft and you need 2 coats so one bottle will do about a 24 ft boat. The amount of Algae Strip is dependant on the amount and type and age of the growth plus the size of the boat. Barnacles will require much more product to remove than algae and heavy old growth will require more than fresh light growth or stains. One bottle should be enough to remove light growth from a 20 to 25 ft boat. Barnacles could take 3 to 4 bottles for the same size boat.

We do not recommend using Algae Strip on Aluminum as it will eat the aluminum. A much better product is Algex. It is made especially for removing algae from aluminum without damaging the metal. You may also want to try our Alumabrite to clean and brighten the pontoons.

Algae Strip is an acid based fiberglass boat cleaner and if applied or dripped directly onto the bunks or the trailer will cause damage. Besides cleaning the bottom of your boat, you have two other issues; one is protecting the trailer against damage and the second is cleaning the parts of your boat that are resting on the bunks.

The solution is quite simple and is covered at some length in another section of this blog under "Getting Under the Trailer Bunks". Once you have the trailer lifted off the bunks, you can protect your trailer with plastic sheeting or plastic garbage bags. Dollar stores sell inexpensive plastic sheeting used as drop cloths for painting which will work for this purpose.

Algae Strip works very aggressively to remove marine growth from fiberglass but is inhibited so it will not damage the fiberglass. It also biodegrades rapidly when reacting with marine growth or when rinsed with water so although the active cleaner can cause damage to your trailer the effluent will not and will not damage the environment.

Another alternative for cleaning the bottom is Green Genie. It is a new formulation that uses organic salts instead of acids. It is more environment friendly but not so aggressive. It works just as well but takes a bit longer (30 to 60 minutes instead of 15 to 30 minutes for Algae Strip). It has other advantages of being safer to use and can be sprayed on as well as applied with a paint roller. You should still protect your trailer as all heavy duty cleaners can cause damage to the bunks and finish.

If your boat is aluminum or if you have metal parts that you are trying to clean, including the propeller, or painted lower units of stern drives or outboards, I suggest that you use Algex as it is intended for cleaning metal without damage. Algae Strip can darken stainless or bronze and can corrode aluminum. After cleaning the marine growth and stains, it makes sense to protect your boat against reoccurrence of attachment of algae, zebra mussels, barnacles etc. I recommend that you deep clean the bottom with Boat Scrub to remove any residue, scuffing, oxidation etc. and then protecting the bottom with VS721 Bottom Coat. You need 2 coats. You can apply one now and the second in the spring before launch. VS721 will reduce the attachment of marine growth and seal the pores in the fiberglass to protect against osmosis blisters. Other benefits are improved performance and reduced fuel consumption. VS721 is recommended by boat manufacturers to prevent osmosis blisters.

Algae Strip will attack and remove some of your bottom paint, plus it will streak it. It will remove the marine growth, but you will probably have to repaint. If you have marine growth you may not have too many options. Algae Strip is definitely easier than scraping and sanding.

The problem is called Osmosis Blisters or Boat Pox. This is not caused by Algae Strip, but by water penetrating through the gelcoat on the hull of the boat and reacting with residual chemicals in the fiberglass. He obviously did not notice the problem before he cleaned the bottom because it was covered by marine growth. The cause is either a manufacturing defect or lack of protection by the boat owner. If he had used VS721 Bottom Coat to protect his hull, it would have sealed the pores in the gelcoat and he would not have this problem.

Yes, Algae Strip is an acid based fiberglass cleaner and it will damage your driveway. The acids will biodegrade rapidly on contact with water, so if you absolutely must clean your boat on the driveway, I would suggest laying down a plastic drop cloth and keep it flooded with water until you are done. Much of the acid will be consumed by the marine growth that you are removing, but there is always the danger of it dripping onto the ground, or in your case the driveway.
When you are through, make sure that you rinse your boat bottom, trailer and driveway with copious amounts of water until all is clean. You may also want to protect your trailer with plastic sheets or garbage bags or at least rinse it well with water to lessen the effects of the acids.
Algae Strip is inhibited so it will not damage the fiberglass on your boat.
We recommend that you use Algex on your outboard or lower unit as it is designed to clean marine growth from aluminum without damaging or pitting it like Algae Strip will. Algae Strip is for fiberglass only.