Reef Strontium Dosing Guide: SPS Growth and Dosage
Strontium sits just below calcium on the periodic table and behaves like its smaller cousin – skeletal tissue in hard corals contains it, and depletion tracks calcium demand in most systems. This reef strontium dosing guide from Gensou Aquascaping at 5 Everton Park covers targets, dose maths, and the ongoing debate about whether modern salt mixes need supplementing at all. Singapore SPS keepers running aggressive growth tanks almost always do.
Where Strontium Sits in the Reef
Natural seawater contains around 8 ppm strontium. Scleractinian corals incorporate it into aragonite at roughly the same rate as calcium, meaning every gram of skeleton deposited pulls proportional strontium out of the water column. Fast-growing tabling Acropora in a 200 litre SPS tank can strip 0.3 ppm per week.
Target Range
Aim for 7-10 ppm. Below 5 ppm, skeletal growth slows and older Acropora develop a chalky appearance at branch tips. Above 15 ppm you risk antagonising calcium uptake and discoloured polyps. ICP-OES is essentially mandatory here because hobby test kits for strontium are unreliable; see our reef tank icp oes test interpretation guide.
Is Dosing Necessary?
Tropic Marin Pro Reef, Red Sea Coral Pro and Aquaforest Reef Salt all deliver 7-9 ppm out of the bucket. A reefer running 10% weekly water changes on a low-bioload mixed reef may never need supplementary strontium. SPS-dominant Triton-method systems running smaller water changes usually require regular dosing within six months.
Calculating Your Dose
Strontium chloride hexahydrate (SrCl2.6H2O) is the standard source. Roughly 3 g dissolved in 100 ml water gives a 10% stock solution. One millilitre of that stock raises 100 litres of tank water by approximately 0.1 ppm strontium. A tank testing 5 ppm with 300 litres of net volume needs around 15 ml of stock to reach 10 ppm, split over a week.
Dosing Alongside Calcium
If you run calcium reactor media or a two-part system, strontium often rides along passively because aragonite media and commercial part B contain trace strontium. Monitor quarterly and top up only when ICP shows a downward trend across two consecutive reports. Browse our two part dosing guide reef tank for the companion calcium and alkalinity routine.
Symptoms of Deficiency
Slowed linear extension is the headline symptom, visible as tabling Acropora that stops pushing its rim. Coralline algae encrusting slows too, since coralline uses calcium carbonate chemistry similar to corals. Fish and inverts show no direct symptoms.
Symptoms of Excess
Beyond 15 ppm, Acropora polyp extension shortens and tissue browns at the base. Tridacna clams may close more frequently. Correct by stopping dosing and letting natural water changes bring levels down; do not use sequestering resins, which also strip useful trace elements.
Interaction with Other Elements
High strontium competes with calcium at uptake sites. Keep calcium at 420-440 ppm before pushing strontium toward the upper end. Barium, another group-2 element, occasionally drifts alongside strontium in old tanks – if your ICP shows barium above 0.02 ppm, recheck your salt mix brand.
Frequency and Automation
Daily micro-doses via a peristaltic pump deliver smoother chemistry than weekly slugs. If you already run dosing pumps for calcium and alkalinity, add a third line for strontium stock rather than tipping it in manually. Our best dosing pumps reef tanks article covers the Kamoer and Jebao units that most Singapore reefers rely on.
Pairing with Trace Elements
Strontium sits in the major ion category, not trace, so keep it separate from any broad trace cocktail you dose. Mixing strontium stock with iron or manganese stock causes precipitation within hours. Use dedicated bottles and rinse dosing tips weekly to clear crystalline buildup.
Local Sourcing and Cost
Strontium chloride is available from Singapore reef retailers at around $20 SGD for 500 g, enough to run a 300 litre SPS tank for a year. Aquaforest Component Sr+, Tropic Marin Pro-Coral Strontium and Brightwell StrontiGro are the bottled options if you prefer ready-mixed solutions.
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