Reddit mentions of Tetra Pond Air Pump Kit, Provides Vital Oxygen to Pond Water (19706)

You're 'getting' a 275g pond, but you need a liner. Just curious, but where did you get that gallon number from? Volume of the hole I assume?

Either way, there is only one thing you need to understand about ponds, but it's a big thing and has many branches of understanding.

The Nitrogen Cycle

Essentially, Fish waste (liquid) is Ammonia. Ammonia is converted by biofiltration (bacteria colonies) into Nitrates and Nitrites. These two plant soluable forms of Nitrogen are plant food.

Dealing with this liquid waste and its conversion into plant food is the fight against algae. If you have enough plants doing their job then you won't have enough plant food for the algae. If you don't have enough plants you will have algae growth.

That's all biology. Next is technical. You have three distinct types of filters you need to have to keep your pond clean.

• Mechanical: Something to catch all the floaty bits: Leaves, fish poo, etc.
  
  
• Biological: Something that holds the bacterial colony that converts the Ammonia to Nitrates. This is usually a bag of lava rock, bio balls, etc. This is pretty easy because the bacterial colonies live everywhere in the pond, it's just nice to have something around the pump that also does this job.
  
  
• Phytological: Plants. Lots of 'em. In general you need ~20-50% of your pond surface area as plant filtration. The more the better, and the more active plant filtration the better. An example of active plant filtration is having a waterfall with a tub attached to it. The water is pumped to the waterfall barrel, which then flows through the plants, then falls back into the water. This is opposed to passive plant filtration, which is just plants in the pond where they just filter whatever water and nutrients that come their way. Active plant filtration does make a huge difference.
  
  So, imaging your pond, you have an amoeba shaped thing full of water. On one side you have your pump and on the other side you have a waterfall weir (this is a good example of one with a slot for a filter pad - mechanical / biological filtration, though personally I like to have a Rubbermaid Stock Tank with a bulkhead fitting and a 3" PVC tube coming out for the spillover. Easy and provides a fantastic area for plant filtration). The placement of the pump and the waterfall on opposite ends of the pond means you get a good water flow. No dead zones, etc.
  
  Also, point of consideration, if your pond is 275g you should get a pump no smaller than 300gph or thereabouts. You want to cycle the pond at least once per hour. Moving water helps the filtration.
  
  Next, and of secondary importance, is to make sure you have an adequate Dissolved Oxygen content. This is usually maintained by having a waterfall, but if you don't have that you can get an airstone or aerator. Something like this, but obviously not so large. But, if you have a decent waterfall or fountain you will be fine.
  
  Anyway, if you have these three types of filtration, mechanical and phytological being the most important, and a good pump, you will have a happy pond.