Do I need to use pond foam between the rocks?

No, you do not need to use pond foam or expanding foam between the rocks, however you should. Expanding pond foam is recommended to hold the rock in place and help direct the water to the desired path. Although foam is an added expense we suggest using foam between and behind most boulders, rocks and even gravel to keep the rocks in place and prevent them from slipping. Pond foam should be used to secure the rock to the liner, other rocks and to fill any voids behind the rocks. Doing this will create a better looking water feature, a longer lasting water feature and a safer water feature for you and any animals.

Using expanding pond foam can be tricky at first, but once you use it a few times you will pick up the skill and know how much and where to apply the foam. The pond foam will stick to just about anything it touches so we suggest wearing old clothes and gloves. The foam is expanding so a little dab will often triple in size, you can always add a little more after the first bit cures.

This wall is approximately 2.5′ tall and completely secure.

We have installed a fish cave which will offer a hiding area for the fish.  Applying foam between these rocks will lock them together making one strong wall and will prevent one of the rocks from slipping out and allowing the entire wall to collapse.  Using foam in between the rocks will fill much of the void which will be between the rocks. These voids can potentially be bad for the pond. sediment such as leaves and fish waste will accumulate and break down never having a chance to get make its way into the filter. This not only will create a nutrient abundance and potential cause algae blooms but can also provide an area for harmful parasites to thrive.