A pond built deep enough and filtered hard enough to keep fish alive

A properly filtered koi pond runs $12,000 to $20,000, and a larger one with a connected stream $20,000 to $35,000. Small ponds and pondless features start around $3,000 to $15,000, mid-size ecosystem ponds are $6,000 to $10,000, and estate schemes with multiple water bodies run $30,000 to $50,000 and up. Filtration capacity and rock volume move the price more than surface area does.

Three feet minimum, and four is better. Depth is thermal mass: a shallow pond heats right through in a 100-degree August, dissolved oxygen collapses and koi suffer. Depth also gives fish refuge from herons, which take koi from shallow water routinely here. Shallow ponds are cheaper to dig and are the single most common reason a Montgomery County koi pond fails.

Weekly: check the skimmer basket, top up for evaporation, and observe the fish — behaviour is the earliest warning of a water-quality problem. Monthly: test water chemistry, rinse mechanical filter media, trim plants. Annually: a partial clean-out, usually early spring, and a pump and aeration service. It is a real commitment, comparable to a swimming pool, and worth being honest about before building one.

Yes, in a pond built for it. They need depth for stable temperature, continuous aeration because warm water holds less oxygen, filtration sized to their waste load, and shade over part of the surface. Koi handle our winters without difficulty. It is August that kills them, and always in ponds that are too shallow, under-aerated or over-stocked — usually all three.

A koi pond is engineered around the fish: greater depth, bottom drain, skimmer and heavy mechanical and biological filtration, usually with minimal gravel because it traps waste. An ecosystem pond uses plants, gravel and bacteria to do most of the filtering, looks more naturalistic, and carries a much smaller fish load. Neither is better; they answer different questions, and the number of fish you want decides which one you are building.

Fewer than most people expect. A common working guide is around 250 gallons per adult koi, since they reach 18 to 24 inches or more and produce a great deal of waste. Over-stocking is the fastest route to poor water quality, and it cannot be filtered around indefinitely. We size the filtration to the adult load you actually want, which is a conversation worth having before excavation rather than after.

A properly built one does not. Mosquitoes breed in still water, and a pond with continuous circulation, a skimmer and surface movement from a waterfall gives them nowhere to lay. Fish eat larvae as well. The ponds that breed mosquitoes are the neglected ones where the pump has failed — which is also when everything else starts to go wrong, so it is a useful signal.

Very little here, which is one of the advantages of this climate. Koi slow down and stop feeding below about 50 degrees, so feeding stops rather than tapers. Circulation usually keeps running. Our winters rarely trouble a pond of adequate depth; the harder season is summer, and the design decisions that get you through August are the ones that matter.

Frequently, and it is often the better value. Most ponds we are called to are structurally sound but too shallow, under-filtered and badly edged — all three are fixable. We deepen the main zone, add or resize filtration, install a bottom drain and skimmer where there is none, and re-detail the edges so the liner disappears. Renovation typically costs well under a rebuild.

A garden pond generally does not need county permitting, but covenanted communities often review water features. In The Woodlands that means a Development Standards Committee submission and ARC approval before work begins. We check your covenants and prepare the submission as part of the project, because a pond built without approval can be required to come out — an expensive way to learn the rule.

Three feet minimum, and four is better. Depth here is about summer heat rather than winter freeze. A shallow pond in Montgomery County can swing ten degrees in a single day, which stresses fish and crashes dissolved oxygen exactly when they need it most. A deeper volume holds temperature steady and gives koi a cool layer to retreat into in August.