Concrete vs. Fiberglass Pool: Does Leak Detection Change?

After twelve years of dragging gear from Palm Harbor to Land O’ Lakes, I’ve heard it all. I’ve seen homeowners convinced their pool has a catastrophic structural failure when, in reality, they just need to stop blaming the Florida sun. If I had a nickel for every time a customer told me, “It’s just evaporation,” without running a simple test, I’d be retired on a boat in the Gulf by now.

When you’re dealing with a loss of water, the material of your pool—whether it’s concrete (gunite), fiberglass, or even vinyl liner—dictates the strategy, but the goal remains the same: stop the waste. Today, we’re breaking down the differences between concrete pool leak detection and fiberglass pool leak detection, and why you should never, under any circumstances, start digging up your backyard based on a guess.
The “Evaporation Myth” and Your First Step
Before we talk about technology, we need to talk about the most common annoyance in my line of work: people who blame the Florida heat for a drop of two inches in a single night. Listen to me closely: that is not evaporation.

In our humidity, even on a scorcher of a day in Wesley Chapel, you might lose an eighth of an inch, maybe a quarter if it’s exceptionally windy. If your water level is dropping faster than that, you have a leak. My first question to you is always the same: How much water have you added in the last 24 hours to keep it level?

Before calling for a professional, perform the Bucket Test. It’s the only way to silence the “it’s just the weather” argument.
The 24-Hour Bucket Test Protocol Bring your pool water to the normal operating level. Fill a five-gallon bucket with pool water about 5 inches from the top. Place the bucket on the first or second step of the pool (so it’s submerged, but water won't splash in). Mark the water line on the inside of the bucket and the water level of the pool on the outside. Wait 24 hours. If the pool water level has dropped significantly more than the water inside the bucket, you have a leak. Concrete vs. Fiberglass: The Detection Differences
While the goal is the same, the mechanics of a leak differ based on the pool shell. Here is how we approach the two most common types in the Tampa Bay area.
Concrete Pool Leak Detection
Concrete pools are notorious for structural stress cracks. Over time, the settling of our sandy Florida soil can cause hairline cracks that aren't visible to the naked eye but swallow thousands of gallons a month. In concrete, we look at:
Skimmer throats: The expansion joint between the concrete and the plastic skimmer is a classic failure point. Light niches: If the conduit hasn't been properly sealed, water will track behind the fixture. Structural cracks: These require precise dye testing to confirm they are actually pulling water. Fiberglass Pool Leak Detection
Fiberglass is a single, molded shell. It’s generally more resistant to the settling issues that plague concrete, but it has its own vulnerabilities. Fiberglass pool leak detection often focuses on:
Fittings and returns: Because fiberglass is rigid, the fittings (jets, lights, drains) are the most common spots where the seal breaks. The “bulge” factor: If a fiberglass pool leaks, the water escaping into the surrounding sandy soil can cause the shell to shift or bulge. Feature Concrete Pool Fiberglass Pool Common Leak Source Structural cracks, plumbing, skimmer joints Fittings, light niches, main drain Detection Method Dye, pressure, acoustics Pressure, acoustic/listening, dye Florida Soil Impact Settling creates cracks Shifting causes fitting strain Our Non-Invasive Workflow
At companies like Level Up Leak Detection, we believe that digging is a failure of diagnostic effort. You shouldn't have to ruin your pavers or your landscaping because someone "thinks" the pipe is broken under the deck. We use a step-by-step, non-invasive approach.
1. Acoustic Detection
We use the LeakTronics acoustic detection system. By using high-sensitivity underwater microphones, we can actually "hear" the sound of water escaping a pressurized pipe. It’s like using a stethoscope on your pool plumbing. If there’s a break in a line, we can often pin it down to within a few inches without ever touching a shovel.
2. Pressure Testing
We isolate specific sections of the plumbing—the return lines, the main drain, and the skimmer lines. By plugging these lines and pressurizing them with air or water, we can determine exactly which line is losing pressure. If the line holds pressure, we know the leak isn't there, and we move on. It’s a process of elimination that saves you time and money.
3. Dye Testing
Once we’ve narrowed it down to the shell, we use specialized dyes. In a concrete pool, this helps us differentiate between a cosmetic surface crack and a structural one that is actively drawing water out of the pool.
Florida-Specific Challenges: Sandy Soil and High Water Tables
Working in areas like New Port Richey and Wesley Chapel, we have to contend with high water tables. When a pool leaks, the water doesn't just disappear; it enters the surrounding soil. If the water table is high, the groundwater can actually push into the pool during certain seasons, which can mask a leak entirely.

Furthermore, our sandy soil is unforgiving. If you have a significant pipe leak, that sand can be washed away, creating a void under your pool deck. This leads to sunken pavers and, eventually, slab cracks. This is why you shouldn't put off a leak test. A small drip today becomes a major structural headache tomorrow.
Why You Need a Professional
I see it every week: a homeowner buys a cheap dye kit online, tries to fix a light niche with silicone they bought at a big-box store, and ends up making the leak worse. Or worse, they hire a "pool guy" who uses "scare tactics," claiming they need to dig up the entire patio because the leak is "probably" under the concrete. That’s laziness. If you aren't using professional-grade tools like those provided by LeakTronics, you are guessing, and guessing is expensive for you.
Summary Checklist for Pool Owners
If you suspect a leak, don’t panic. Follow this checklist:
Run the Bucket Test: Confirm the water loss isn't evaporation. Check your equipment: Is there water pooling around your pump or filter? Is your auto-fill constantly running? Keep a log: Note how much water you add and how long it takes for the pool to drop again. Call a specialist: Find a professional who prioritizes non-invasive methods. You want someone who uses acoustic gear and pressure testing, not a backhoe.
Stop stressing over your pool dye test vs pressure test https://www.levelupleakdetection.com/greater-tampa/pool-leak-detection water bill and stop guessing about the source. Whether you have a concrete pool that’s settling or a fiberglass shell with a loose fitting, there is a scientific way to find the leak without tearing up your backyard. If you're in the Tampa Bay area and want an honest, systematic assessment, reach out for a free estimate. Let's find out where that water is actually going.