Controlling Algae and Investigating Fish Loss in a Small Pond

Identifying the Algae Type

Not all algae are the same. Short, fuzzy algae on rocks and plants is generally beneficial attached algae. Long, stringy "hair algae" is tougher to control. Most algae-eating fish and snails ignore hair algae. For attached algae, a plecostomus may help, but they die below 50°F. Rosy barbs (tropical) are one of the few fish that consume hair algae.

Predator Attack: The Likely Cause of Fish Loss

Finding half your fish missing, with one partially eaten, strongly suggests a predator. Herons usually swallow fish whole. In San Jose, raccoons, cats, or other mammals are probable culprits. Netting the pond is the most reliable defense.

Pond Size Matters for Koi

A 200-gallon pond is far too small for koi, which can reach 3 feet and require over 1,000 gallons. Overcrowding degrades water quality and fuels algae growth. Consider rehoming koi to a larger pond and keeping only small, suitable species like mosquito fish, rosy red minnows, or goldfish.

Comprehensive Algae Control Strategy

Long-term algae control relies on balance: abundant aquatic plants to compete for nutrients and provide shade, minimal fish stocking, efficient filtration, healthy beneficial bacteria colonies, and possibly barley straw. Visit this algae resource for detailed guidance.