Pond Fish
Pond liners, pumps and filters in Costa Rica.
A garden pond in Atenas lives or dies by three pieces of kit: a liner that holds water, a pump that never stops and a filter that keeps the water from turning to pea soup in the afternoon sun. Liners, preformed ponds, fountain and waterfall pumps, pressure filters and UV clarifiers are listed new and pre-owned, often as a whole set when someone fills a pond in or moves house. One afternoon downpour can bring a pond over its rim, so a screened overflow pipe is part of the kit, not an extra.
A preformed pond or a liner in a hole you dug:
those are the two ways to hold the water. A preformed pond is a rigid plastic or fibreglass shell with the shelves already moulded in. It goes in fast, but you live with its shape and depth. A flexible liner takes any shape you can dig. EPDM rubber is the one pond builders prefer because it lays into curves without fighting back; PVC is cheaper and fine for a modest pond; black HDPE geomembrane, the sheet farms use for reservoirs, is the toughest and the stiffest, and big pieces are heat-welded rather than folded. Under any liner goes a geotextile underlay, so stones and roots do not wear through from below. Glass tanks and stands sit with aquariums and aquarium accessories, and heaters, nets and transport bags with aquarium fish.
Sizing a pond pump, a filter and a UV clarifier:
a pump is rated for flow, but every bit of height it has to lift the water to reach a waterfall costs some of that flow, so check the figure at your waterfall’s height, not the one on the front of the box. A pond with real volume wants a box or waterfall filter, or a pressure filter that can sit buried beside the pond and push water uphill. A UV clarifier is what stops green water in full sun, and many pressure filters have one inside. Solar fountain pumps save running a cable to a spot with no socket, but they slow or stop when cloud comes over. A small pump-and-filter kit for a garden pond starts around ₡70,000 new, and a pump strong enough to drive a proper waterfall runs to ₡250,000 or ₡300,000. Used liners sell for far less than their area suggests, because a liner is cut and creased to the pond it came out of and only suits a hole of similar size; a pump holds its value only if you can see it running.
A downpour and the overflow pipe:
heavy afternoon rain fills a pond faster than it evaporates, and without a way out the water lifts over the lowest point of the rim, takes the edging stones with it and undermines the bank. A pond in Turrialba, or anywhere afternoon downpours are routine, wants an overflow pipe set just below the edge with mesh over its mouth, and a rim built up above the surrounding ground so garden runoff and fertiliser drain around the pond rather than into it.
Sun-cracked edges and taped cables on a used pond kit:
unroll a used liner on the lawn and look at the strip that sat above the waterline: wherever the edging stones left it bare to the sun, it goes brittle and cracks first. Hold it up to the light to find pinholes where a stone rubbed through. On a preformed shell, check the shelves and rim for stress cracks and warping. Follow a pump cable from end to end: it lives underwater, and a cut sealed with electrical tape is a reason to walk away. A pressure filter that baked in the sun can crack around the lid, so look at the seal and clamp, and check that spare sponges and bulbs for that make are still easy to get.
Rolling up a pond before the buyer comes:
for a liner, give the original uncut size and the material; for a preformed pond, its length, width and depth. Name the pump’s make, its rated flow and the height it was lifting to, and say whether the filter has a UV built in. Photograph the liner spread flat and film the pump running. A folded EPDM liner is heavier than it looks, so whoever collects it needs a second pair of hands and a pick-up. And roll it up dry: a liner left holding rainwater in a garden in Atenas is full of mosquito larvae within the week.