How to safely remove stains on a fishpond berm
Q: Three years ago, we bought a house with a backyard brick berm and fishpond that are probably around 20 years old. We also have a brick wall surrounding our entire backyard. Mineral stains have appeared on the brick, but only over the pond. I’ve read on the internet that I could use baking soda or vinegar to remove the deposits, or power-wash them off. But my husband and I are wary of doing anything that could harm the fish that live in the pond. We plan to ask the company we hire each spring to clean the pond for advice. What do you recommend as a way to remove the white spots without harming the fish? Assuming we are able to clean the brick, are there steps we should take to keep this from happening again?
A: The white spots are efflorescence, a crust that develops when water laden with mineral salts moves through the bricks and evaporates, leaving salt crystals behind. It’s ugly but usually doesn’t cause damage, so you can take your time figuring out a solution. The salts can come from many different things, including the clay in the bricks or the Portland cement, sand or even water used to make the mortar between the bricks. Because the deposits in your yard are showing up only on brick that is holding back soil, the salts are probably in the soil or in fertilizer used in the planting beds.
Because you already hire a company to clean your pond each spring, dealing with the efflorescence at the same time is definitely the way to go. To ensure that the cleaning doesn’t harm the fish, ask the company to scoop them out and temporarily house them in a container with lots of clean water. Don Jump, owner of Harmony Ponds in Lorton, Virginia, said the company has a 1,000-gallon tank they use for this. Saving the pond water, along with the fish, also helps them because it avoids an abrupt change in the chemistry of the water. And getting the fish out of the way safely before you tackle the efflorescence is a lot less stressful than doing it when the water is already contaminated and you’re racing to keep the fish from dying.
With the fish and water out, the pond cleaners can remove the mineral crust. The Brick Industry Association, a trade group, recommends starting by scrubbing with a dry, stiff brush, then switching to a brush with water and finally to a cleaner formulated to remove efflorescence from masonry. Jump said his company starts with these steps. If the efflorescence is new, a brush usually scrubs it right off, he said, and if it’s been there for about six months, a cleaner usually works. “But what we’re usually dealing with is years old,” he said. For that, his crew turns to an angle grinder fitted with a wire wheel, which the team uses as gently as possible. He estimated cleaning the bricks would take about one hour, which would add $160 to the spring-cleaning bill for customers who have signed a contract for seasonal pond cleaning. The spring-cleaning service fee ranges from around $240 for a small pond like yours to $1,000 or more for large, complicated ponds, Jump said. Customers who want one-time cleaning pay a higher hourly rate of $240.
Waiting until spring to deal with the efflorescence would save you money and would probably make the cleaning last longer. Efflorescence tends to show up more in the winter than in the summer, because the bricks tend to stay damp longer in cold weather, allowing more salts to move through. And, as the Brick Industry Association notes in a paper about dealing with efflorescence, “It is usually not advisable to wash efflorescence off the brickwork except in warm, dry weather, since washing results in the presence of considerably more moisture, which may bring more salts to the surface of the brickwork.”
As for fixing the underlying problem, you would need to keep moisture from moving through the bricks. What would have been easy during construction is more work now. You would need to excavate the soil behind the brick and either waterproof the back of the brick or line the planters so moisture can’t seep out through the front. You’d still need a way for excess moisture to escape, however, both to keep plants healthy and to keep waterlogged soil from pushing out the bricks. A common solution is to install weep holes through the wall at the base. Outfitted with pipes that slant downward toward the front of the wall, the weep holes would allow water to drip out beyond the face of the brick. A landscaping company that does masonry work can offer advice.