Buying a Second-Hand Reef Tank: What to Check Before You Commit

The Smart Way to Get Into Reefing

A Red Sea Reefer 250 retails for about £1,200. On the used market? £500–700 in good condition. That's £500+ saved — money far better spent on lighting, a good skimmer, or livestock.

Tanks, stands, and sumps are built to last decades. Most are sold because the owner is upgrading, downsizing, or leaving the hobby — not because anything is wrong. But knowing what to inspect is essential.

The Silicone Seals

The most important check. The silicone is the only thing preventing a catastrophic leak.

Clarity — good silicone is clear or slightly translucent. Yellowed or opaque suggests UV degradation
Adhesion — should be firmly bonded to both panels. Any delamination is a red flag
Uniformity — consistent width and thickness. Thin spots or gaps are weak points
Flexibility — press gently with a fingernail. Good silicone has give. Rock-hard and brittle means it's past useful life

Resealing is possible but takes a full day plus curing time. Factor this into pricing negotiations if seals look questionable.

Glass Condition

Scratches — minor external ones disappear when filled. Deep internal scratches (from magnetic cleaners trapping sand) are more concerning
Chips — check all edges, especially near drilled holes. Chips near structural joints are a concern
Clarity — cloudy patches from calcium etching are cosmetic but annoying

Cabinet / Stand

Check for water damage, warping, swelling in MDF, rust on fixings
Inspect waterproof interior coating
Place a spirit level on top — the surface must be flat. Warped cabinets mean unlevel tanks and eventual seal stress

Plumbing, Overflow, and Sump

Check bulkhead gaskets for cracks
Look for silicone separation on overflow boxes
Inspect sump baffle seals
Ensure the sump can hold drain-back volume if the return pump stops

Key Questions for the Seller

How old is the tank?
Has it ever leaked or been resealed?
Has it been stored empty? (Poor storage causes seal issues)
Can it be filled for a leak test before collection? — any honest seller should agree to this

Rough Pricing Guide (UK, good condition)

Fluval Evo 52L: £80–120
Red Sea MAX Nano: £250–350
Red Sea Reefer 170: £400–600
Red Sea Reefer 250: £500–700
Red Sea Reefer 350: £700–1,000

Prices fluctuate seasonally — spring tends to be pricier, winter often cheaper.

Browse second-hand tanks and complete reef setups from UK sellers — the best deals go quickly, so checking regularly pays off.

What's the best or worst used tank deal anyone has found? Bargain stories and cautionary tales are equally useful.