How to Raise Alkalinity Without Crashing pH

Here's a common way to lose half a frag rack overnight. Alkalinity drops to 5.2 dKH, so you dump in a large slug of buffer to get it back to 8 dKH in one hit. By morning, three SPS colonies have gone pale and started sloughing tissue. This is one of the most common and preventable mistakes in reef keeping, and it comes down to moving alkalinity too fast rather than too slow.

Why Fast Alkalinity Swings Crash pH and Kill Coral Tissue

Alkalinity and pH are linked through the carbonate buffering system in your water. When you add a large dose of buffer, you shift the carbonate to bicarbonate ratio quickly. This causes a rapid pH swing, usually a spike followed by a slower drop as the system re-equilibrates. Coral tissue does not tolerate rapid chemistry shifts well. The result is often RTN, rapid tissue necrosis, where healthy looking coral loses flesh from the base upward within hours.

The safe rule most experienced reefers follow is no more than 1.0 to 1.4 dKH change per 24 hours, and ideally closer to 0.5 dKH for sensitive SPS systems. Slow and steady beats fast correction every time, even if your test kit says you are technically low.

Alkalinity Dosing Schedule: A Slow, Practical Approach

Start by identifying your baseline. Test alkalinity daily for at least four days before making any dosing changes. This gives you a real trend rather than a single reading that might be an anomaly.

Week One: Establish the Baseline

• Test KH every day at the same time, ideally before lights on.
• Log results in a notebook or app. Look for consistency, not perfection.
• Do not dose anything extra yet unless KH is below 6 dKH.

Week Two: Begin Micro-Dosing

Once you have a baseline, calculate the dose needed to raise alkalinity by no more than 0.5 to 1.0 dKH over 24 hours, split across two or three smaller doses rather than one large one. A dosing pump such as the Kamoer range makes this straightforward because you can program multiple small doses spread through the day rather than manually dosing once.

For two part dosing reef tanks, Red Sea Reef Foundation A and B (500ml, 30 to 31 AUD each) is a reliable combination that most Brisbane reefers already run alongside their calcium and magnesium supplementation. Aquaforest's Stone Fix 1500g is another option many use for stony coral systems needing consistent carbonate hardness support.

Week Three Onward: Fine Tune and Automate

By week three you should have a repeatable dose that holds KH steady within 0.2 to 0.3 dKH day to day. This is when a controller pairs well with your dosing pump, letting you set reminders or alarms if alkalinity drifts outside your target range.

Kalkwasser vs Dosing Pump: Which Suits a Slow Correction?

Kalkwasser (limewater) raises alkalinity and calcium together and has the side benefit of nudging pH upward, which some tanks running low pH benefit from. It is dosed via a calcium reactor or drip system and works well for smaller to mid sized systems where evaporation top off volume matches dosing needs closely.

A two part liquid dosing pump setup, using Red Sea Reef Foundation or Continuum's KH Buffer range, gives more precise control over volume and timing, independent of your ATO schedule. For anyone running an automatic top off unit already, pairing it with a dedicated dosing pump avoids the guesswork of kalkwasser saturation and mixing.

Testing Alkalinity Daily: What to Track and When

Daily testing during a correction phase is not optional. Use a reliable KH test kit from our Prices are accurate at the time of publishing and are subject to change. Check the product page for the current price before buying.