Glass vs acrylic tanks

Glass is heavier, cheaper, and scratch-proof. Acrylic is lighter, clearer, and fragile to algae scrapers. Which matters depends on tank size and where it's going.

This decision gets simpler once you know the tradeoffs. Glass wins on scratch resistance and cost. Acrylic wins on weight and impact strength. Everything else is a second-order effect.

Weight

A glass aquarium weighs roughly twice as much as an acrylic tank of the same dimensions, empty. A standard 55-gallon glass tank weighs about 35 kg (78 lbs) before you add water, substrate, or anything else. The same volume in acrylic weighs around 17 kg (38 lbs). Once filled, water dominates the total weight and the difference matters less in absolute terms, but the empty weight matters for setup, moving, and what your stand and floor need to handle.

For tanks under 100 gallons, the weight difference rarely changes the decision. You can carry either to the stand with one other person. Over 100 gallons, glass gets quite difficult to move. A 180-gallon glass tank weighs around 80 kg empty. Acrylic at that size is half that, which is the difference between needing two people and needing four.

The tank volume calculator gives you the water weight for any dimensions. The tank weight calculator estimates total weight including glass or acrylic panels, substrate, and hardscape. Use those numbers when checking floor load.

Scratch resistance

This is where glass dominates. Glass has a Mohs hardness of about 5.5. Acrylic is around 3. Sand, gravel, and dried mineral deposits all score above 3 on that scale. One grain of sand caught in a magnetic algae scraper will leave a visible scratch on acrylic. That scratch is permanent until you drain the tank and polish it out with a specialized buffing kit.

Glass shrugs off the same incident. You can clean glass with a razor blade, a rough sponge, or a magnetic scraper with trapped debris and the glass will be fine. Over years of maintenance, glass panels stay clear. Acrylic panels accumulate fine scratches that scatter light and cloud the view, a condition called "crazing" in older tanks.

Acrylic scratches can be repaired, but it means draining the tank, drying the panel, and working through progressively finer abrasive grits. It takes an hour or more per panel and the results aren't always invisible. Most hobbyists never do it. They just live with the scratches or replace the tank.

Clarity

Brand-new acrylic transmits about 93% of light. Standard float glass transmits around 82%. Low-iron glass (often sold as "ultra-clear" or "Starphire") transmits 91% and eliminates the green tint visible at the edges of standard glass.

In practice, the clarity difference between acrylic and standard glass is visible mainly on large, deep tanks where you're looking through a lot of material. On a 60 cm (24 in) wide tank, most people can't tell the difference. On a 120 cm tank, the green tint of standard glass becomes noticeable, especially from the side. Low-iron glass closes the gap and looks nearly as clean as acrylic.

Acrylic doesn't yellow anymore like it used to. Modern cast acrylic with UV inhibitors holds up well for years under aquarium lighting. Early acrylic tanks from the 1990s and earlier did yellow over time, and that reputation persists, but it's mostly a solved problem with current materials.

Impact resistance

Acrylic is about 17 times more impact-resistant than glass. A rock dropped inside a glass tank can crack a panel. A heater falling against glass can crack it. Acrylic flexes instead of breaking. For homes with young children, or tanks in high-traffic areas, this is a meaningful safety advantage.

Glass fails suddenly and catastrophically when it does fail. A crack propagates instantly and the tank dumps its contents on the floor. Acrylic, when it fails (which is rare from impact), tends to develop slow leaks rather than sudden blowouts.

That said, glass aquarium failures are uncommon. The glass is tempered or at least thick enough for the pressure. Failures usually come from silicone joint degradation after 10-15 years, not from glass breaking. And silicone can be replaced; a cracked acrylic panel cannot.

Cost

Glass tanks cost 30-50% less than acrylic at comparable sizes. A standard 55-gallon glass tank runs $100-150. An acrylic 55-gallon is $200-350. The gap widens with size. A 120-gallon glass tank might cost $350-500. The same in acrylic: $600-1,000 or more.

Custom shapes (bowfront, cylinder, hexagonal) narrow the gap because glass fabrication for non-rectangular shapes is more expensive. If you want a curved viewing panel, acrylic is easier to form and the cost premium shrinks.

The practical decision

For most freshwater hobbyists buying a rectangular tank under 100 gallons: glass. It's cheaper, easier to maintain scratch-free, and the weight difference isn't a factor at that size. Standard glass works. Low-iron glass if you want to spend a bit more for the look.

For tanks over 150 gallons, especially on upper floors where weight matters: acrylic becomes worth considering. Run the numbers through the tank weight calculator to see whether the glass version exceeds your floor's load capacity. If it does, acrylic's lower weight might be what keeps the tank possible.

For tanks in high-traffic areas, rooms with kids, or any situation where impact risk is elevated: acrylic's shatter resistance is a real safety feature, not a marketing claim.

For anyone who hates scratches: glass, full stop. If a visible scratch on the front panel would bother you, do not buy acrylic. You will scratch it eventually regardless of how careful you are.

Long-term ownership experience

Glass tanks are set-and-forget from a material standpoint. The glass won't degrade, discolor, or weaken over decades of use. Silicone seams are the failure point, and resealing a glass tank is a DIY repair that costs $10 in silicone and an afternoon of work. A well-maintained glass tank lasts 15-30+ years.

Acrylic tanks require ongoing surface care. Small scratches accumulate from cleaning (even with acrylic-safe pads), gravel contact, and decorations touching the walls. Minor scratches can be polished out with acrylic scratch removal kits ($10-20), but deep scratches are permanent. Over 5-10 years of regular use, an acrylic tank that started crystal clear may develop a faint haze from micro-scratches that no amount of polishing fully removes.

Acrylic also bows slightly under water pressure over time, especially in larger tanks (over 300 liters) without adequate bracing. This bowing is usually cosmetic (the panels flex outward by 1-3 mm) but can stress joints in poorly designed tanks. Quality acrylic tanks are built with thicker panels and internal bracing to prevent visible flex.

Resale value: Glass tanks hold value better. A used 200-liter glass tank in good condition sells for 50-70% of new price. A used acrylic tank of the same size sells for 30-50% because buyers factor in potential scratches and bowing.

Which to buy

For most freshwater fishkeepers, glass is the practical choice. It's cheaper, scratch-resistant, and lasts indefinitely with minimal care. Choose acrylic when weight is a genuine constraint (upstairs apartments, wall-mounted displays), when you need a custom shape that glass can't easily provide (curved panels, hexagonal, bow-front), or for very large tanks (over 500 liters) where reduced weight simplifies the support structure.

The tank weight calculator estimates the total filled weight of your tank, which is a key factor in deciding between glass and acrylic for floor-load-sensitive locations.