False Uptake

False uptake is when a test reads as if corals used an element, but it actually left the water another way. The Aqua Care Guide™ uses the term for calcium and alkalinity.

The reading looks like normal consumption. The cause is something else.

Why It’s Important

• It leads to dosing you don’t need. With phosphate problems, dosing calcium can show a false uptake of calcium, which prompts more supplementation.
• That extra calcium can feed a cycle in which more bound phosphate forms.
• Calcium taken out by phosphate is no longer in the water column, so calcium falls and corals can be stressed.
• It’s one reason dosing needs differ from tank to tank, even with products made to the typical uptake ratio.

How It Works

The Guide gives two examples:

• Alkalinity removed through pH fluctuation.
• Calcium bound by phosphate, which can settle onto live rock.

The Guide recommends fixing a phosphate problem as soon as possible. AR Phosphate Remover™ removes ionic and chemically bound phosphate and frees bound calcium.

False Uptake and Related Terms

False uptake can look like real calcium uptake or alkalinity consumption on a test. The phosphate version involves phosphate and precipitation onto live rock.

The Bottom Line

False uptake is an element lost to something other than your corals. If calcium keeps falling while phosphate is a problem, deal with the phosphate first. More in Understanding Phosphate in Aquariums.