So i made a small pond out of retaining blocks that i mortered in place and lined the interior with cement mix. It was built on top of an old concrete septic tank access point. The septic tank was sealed like 40-50 yes ago hut it goes like 13 feet deep in the ground and theres no way of removal. Before it was just used as a raised planter bed for flowers. As it is now its about 2.5 feet deep and about 5.5 feet across.

So when initially built, i sealed the concrete with food/aquarium safe silicone that had been thinned with mineral spirits and painted on the interior with a paint roller. This worked well, pond was happy and thriving for about 3 years. Then one spring the blue herons discovered our backyard and by fall, all of or lovely koi friends had become bird breakfast. Let it sit and eventually drained and cleared the plants out when i noticed the silicon was starting to peel. Aftet some research i found that aquarium silicon simply doesnt have the longevity to survive for years outdoors and exposed to sun.

Drained, pressure washed. And am wanting to give it another go. The plan is to add another top layer of retaining blocks after grinding the surface down and lining with fresh cement/mortar to make it about 3 feet deep and add hooks to attach some sort of netting to keep predators out. The problem im finding is tha over time, the top heavy concrete structure thats deeply embedded in the backyard has settled and leans a bit. This makes about a 4-5 inch difference where the water line is at the very brim of the pond one side and a few inches below on the other side. Structurally its sound. My question is without being able to dig beneath to try to raise it to level, what other options do o have ? Advice on how to stop further sinking? ( Our property is on a declining slope and the patio and backyard garage also are having issues with slowly sinking as well but 🤷🏽‍♂️) I bought some pond sealer stuff made specifically for lining outdoor ponds (like epoxy/resin thats paintable) but before i get started i figure id ask advice on solutions for the unlevel waterline. I was gonna take some 5 foot fence t posts and sharpen with a grinder and drive them down at an angle flush against the side thats settling then put in some cement to secure to the base then top with stepping pavers around the pond just to try and prevent further sinking and to make it easier to mow the lawn around the base. But i realize at 8 lbs a gallon this may be a futile attempt pitting backyard diy engineering against the power of nature, is this a lost cause? Should i just give up and fill with dirt and keep strawberries instead of fish? 😞