City of Fresno’s Historic Change in Water Source Affects Aquarium pH

by Tom Lang

Since 1980, Aquarius Aquarium has been maintaining aquariums for clients throughout the City of Fresno (and beyond).  It was a tremendous advantage to be able to change water as a part of our routine and have the pH of our client remain fairly constant between our regular service visits. Most of our clients have us out either monthly or every-other-week, so water chemistry did not vary very much from what came out of the tap.

Historically, the City of Fresno sourced all its water from a network of wells located throughout the city. Giant electric pumps brought up water from the vast aquifer located beneath the city that contains a significant level of carbonate hardness (KH – from the German Karbonathärte – also known as Alkalinity) because the San Joaquin Valley was a great inland sea millions of years ago. The calcium carbonate skeletons of marine organisms are still found in layers far below the land’s surface to this day and, as water has seeped down through these layers over millennia, it picked up carbonates and bicarbonates by dissolving those deposits along its way.

Over many years, our tests routinely measured tap water KH in Fresno in the 8 -10 dKH range when the water was sourced from groundwater. But since 2018 and 2019, the city has introduced more and more treated surface water from the San Joaquin and Kings Rivers into its system. The Southeast Surface Water Treatment Facility (SESWTF) completed construction in 2018 and is being fed with surface water from the Kings River through a newly-constructed 13-mile long Kings River Pipeline.

Soon after the SESWTF came online, our testing indicated a marked decrease in KH readings in nearly all areas of Fresno, bottoming out during the summer of 2019 with some taps testing as low as 1 – 2 dKH.

What low KH means to aquarium owners

When KH is low, an aquarium water’s ability to buffer against an unsafe drop in pH is diminished when measured over time. As the fish produce acidic waste, the tendency is for pH to decrease over time, effectively “using up” the KH. In most cases when San Joaquin Valley groundwater is the source, low to medium stocked aquariums will maintain healthy pH levels without water changes for at least a month. This holds true in the majority of aquariums as long as KH starts at between 5 and 10 dKH in our experience. However, it needs to be said that this is a moving target and that it follows that more fish in any given aquarium will speed up the process of “using up” KH.

While the city will truthfully say our water complies with federal EPA standards, these standards do not specifically take into account how much KH is present in our tap water. The City of Fresno’s own “Recharge Fresno” website made it clear that as more surface water is added to the system, the lower its alkalinity will be. This is due to water from mountain snow run-off contains significant less KH since this water has not seeped down through the San Joaquin Valley floor’s calcium carbonate sediments.