Pool Shell Leak Detection

A dropping waterline doesn’t always mean your pool shell is cracked — leaks can come from fittings, plumbing, or ground movement. Use the bucket test, inspect fittings, and watch where the water level stabilises to pinpoint the source. Fix small shell cracks early, pressure-test plumbing if needed, and call a professional when the cause isn’t obvious.

There’s nothing worse than walking out to your pool and realising the water level’s dropped — again. You top it up, blame evaporation, maybe even the kids splashing too much… but deep down, you know something’s not right.

A slow leak in a fibreglass pool shell doesn’t just waste water — it stresses the structure, creates ground voids, and can even lead to cracking if ignored too long. The good news? Most leaks are fixable once you know where they’re coming from.

Let’s walk through how the pros track down pool leaks, what to check first, and when it’s time to call in expert help.

Key Takeaways

• Not all leaks come from the shell. Plumbing, fittings, or worn gaskets are often the true culprit.
• The bucket test is your first step. It quickly tells you whether water loss is evaporation or a real leak.
• Where the water level stops matters. Stabilisation near a jet, skimmer, or light fitting usually points to a seal issue, not a cracked shell.
• Pump behaviour provides clues. Leaks that worsen with the pump on suggest pressure-side plumbing problems.
• DIY is fine for tiny cracks only. Hairline gelcoat cracks can be patched, but anything leaking water needs professional repair.
• Don’t over-drain your fibreglass pool. Keeping water in the shell helps prevent ground pressure issues and structural stress.
• Fix leaks early. Small leaks create soil voids that lead to shell movement, bigger cracks, and expensive repairs if ignored.
• Professional leak detection saves money. Acoustic tools, dye tracing, and pressure testing find the source precisely — without digging or guesswork.

How to Tell If Your Pool Shell Is Leaking

Before you panic, remember: every pool loses a little water naturally. In summer, evaporation alone can steal up to 5mm a day — more in dry or windy weather. But if your water level drops faster than that, it’s time to investigate.

1. The Bucket Test

The oldest trick in the book, and still one of the best.

1. Fill a 10L bucket with pool water and place it on a step, so the water inside the bucket is level with the pool water.
2. Mark both water levels.
3. Wait 24 hours (pump off).
4. If the pool’s water drops more than the bucket’s, you’ve got a leak.

2. Visual Cues

Keep an eye out for:

• Persistent wet spots or soggy ground near the pool.
• Air bubbles coming from return jets.
• Cracks in tiles or coping around the edge.
• The water level consistently dropping to the same point before stabilising — a classic sign of a shell or fitting leak.

💡Expert tip: Don’t jump straight to “the shell’s cracked.” Around half of suspected shell leaks turn out to be plumbing or fittings.

If you want to prevent these issues before they start, make sure you’re following proper care routines (our guide on pool shell maintenance tips is a good place to start).

When the Leak Might Be in Plumbing, Not the Shell

It’s surprisingly easy to misdiagnose a leak. A pipe under pressure can lose just a few litres a day — invisible, but constant.

Here’s how to tell the difference:

• Leak stops when pump is off? → It’s probably in the pressure side (return line).
• Leak continues when pump is off? → Check the suction side or shell itself.
• Water level stabilises below a jet or light fitting? → Likely a fitting seal leak, not structural.

If you suspect plumbing, a pressure test can confirm it. Professionals use dye, listening devices, or helium testing to isolate the leak within a few centimetres.

💡Pro insight: Fibreglass shells rarely leak on their own unless they’ve been structurally compromised — most “shell leaks” are actually failed fittings or returns set in the shell wall.

What to Do After Finding a Leak

Once you’ve pinpointed the problem area, resist the urge to rush the repair — especially if it’s near plumbing.

💡Expert insight: Fix the cause, not the symptom. Sealing a visible crack without addressing ground voids or pressure loss just delays the problem.

When to Call a Professional for Leak Detection

There’s a fine line between handy DIY and digging yourself into trouble (literally). Call a professional if:

• You’re losing more than 2–3cm of water per week consistently.
• The ground around your pool feels spongy or hollow.
• The water level drops below fittings or skimmers.
• You’ve tried a bucket test and can’t isolate the cause.

Professionals use acoustic sensors, dye tracing, and pressure testing to locate leaks without guesswork — saving you from tearing up paving or over-draining the shell.

💡Pro tip: Always fix leaks early. A $300 detection job today can prevent a $10,000 repair down the line if the shell shifts or delaminates from water loss.

Preventing Future Leaks

Once your pool’s watertight again, a little prevention goes a long way:

• Check fittings annually. Rubber seals harden over time.
• Avoid over-draining. Always leave at least a third of the pool full to maintain pressure balance.
• Keep water chemistry balanced. Acidic water slowly eats at sealants and fittings.
• Schedule professional inspections every few years — especially if you’re on shifting soil.

💡Expert opinion: Most leaks aren’t random — they’re the result of something overlooked. A simple maintenance routine keeps that flawless fibreglass surface watertight for decades.

If your leak turns out to be from a crack in the shell, not the plumbing, check out our full guide on pool shell crack repair for repair methods and long-term prevention tips.

Pool Shell Leak Detection: Find the Source Early

A dropping waterline doesn’t always mean bad news — just that your pool needs a little attention. With smart testing and the right approach, you can spot, confirm, and fix a leak before it becomes serious.

Because when it comes to leaks, guessing is expensive — but finding the source early is priceless.