I Live in phoenix and a friend came across 2 plastic ponds and gave them to me they were both black plastic and had some issues... I used FLEX seal to coat the outsides completely on the inside i used a white rubberized roofing product but i added dark and light pebbles and sand. The finished product came out just like i wanted not black not bright white but a neutral gray mostly. I put them out in direct sunlight for a few weeks then i filled them and emptied them about 10 times over the summer... I used a mild soap and cleaned em both... the bigger round pond went inground and the other formed pond was position about 2 feet above so that I could create a waterfall. I have lots of slate and stone on my property so I stacked flat rocks and used a waterproof glue to hold the rocks together I put a plastic pond liner behind the the water fall so no water escapes. I hid the water pumps in the rock ledge under the waterfall and also the water lines to the upper pond. The filtration pump is placed center for easy access it also has the ability to pump water up to the upper pond to make water fall stronger and it can be set to airiate the water with a fountain... I crossed my fingers and put 6 common feeder goldfish in it hoping that my pond would not kill or poison them.... within 1 week everything turned green! I emptied the ponds cleaned em and then put shade plants around the pond and added water plants to the upper pond and that cleared the water and reduced the green stuff from returning.... The water gets up to 85 °F on hot days and temps drop to 77 at night... the fish are alive and very active.... im gonna see how the winter goes.... I paid like 3 bucks for the fish.... I will add about 12 more goldfish if everything goes well this winter... Oh I also added drop in pumps to help move water around in the upper pond it keeps water from getting warm...