DIY project

How to build a DIY aquarium sump

Intermediate8 steps$120

What you'll need

20-40g tank (used works fine)
1/4-inch acrylic sheets cut to size
Aquarium-grade silicone (NOT bathroom silicone - mold inhibitors kill fish)
Caulk gun
Razor blade or aquarium scraper
Measuring tape + marker
Cleaning supplies
Painter's tape

Step-by-step

Step 1: Plan the chamber layoutSketch on paper: chamber 1 = skimmer (water from overflow), chamber 2 = refugium (chaeto + reverse-cycle light), chamber 3 = return pump. Measure tank width and divide into 3 sections.

Step 2: Cut acrylic bafflesYou need 3 baffles for the bubble trap (panels alternating up/down/up). Plus 2 dividers for chambers. Cut acrylic to tank-width (slight clearance, 1/8 inch each side) by appropriate height.

Step 3: Test fit bafflesDry-fit all baffles in tank without silicone. Mark precise placement on tank glass with painter's tape. Verify spacing of bubble-trap baffles (1-2 inches apart).

Step 4: Clean tank glass + bafflesWipe with isopropyl alcohol. Silicone won't bond to greasy or dirty glass. Remove all dust + handprints.

Step 5: Apply silicone to bafflesRun a thick bead along the bottom + side edges of each baffle. Press firmly into place against tape lines. Smooth excess silicone with wet finger.

Step 6: Cure 7 daysMandatory 7-day cure for aquarium silicone. NEVER fill before 7 days - silicone is still releasing acetic acid that kills livestock.

Step 7: Water test 48 hoursFill with plain RODI water. Check for leaks at baffle joints + tank seams. Run for 48 hours minimum before transferring saltwater + livestock.

Step 8: Plumb and test equipmentAdd return pump in chamber 3, test full flow. Add skimmer in chamber 1, verify water depth matches manufacturer spec. Add refugium light + chaeto.

FAQ

Can I use bathroom silicone for an aquarium sump?

NO. Bathroom silicone contains mold inhibitors (mildewcide) that leach into water and kill fish. Use 100% pure silicone aquarium sealant only.

How long does aquarium silicone take to cure?

7 days for full cure. 24 hours for surface dryness. NEVER fill before 7 days.

What size sump for my tank?

25-40% of display volume is standard. A 75g display benefits from a 30g sump.

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Aquarium-keeping fundamentals

Whatever specific topic brought you here, four fundamentals govern long-term aquarium success: water quality, parameter stability, biological filtration, and species-appropriate husbandry. Skip any one and the others struggle to compensate.

Water quality: ammonia + nitrite at zero, nitrate under 30 ppm freshwater + 10 ppm reef. Test weekly with API or Salifert kits. Use our water parameter checker to score your readings against your tank type.

Parameter stability: stable wrong parameters beat fluctuating ideal parameters. Most fish tolerate a wide pH range if it's stable. Sudden swings of 0.4+ pH or 5+°F kill fish faster than chronic suboptimal values. Use temperature controllers (Inkbird) + automated dosing for consistency.

Biological filtration: the bacterial colony on your filter media + rock + substrate is the engine. Never replace all media at once. Use our filter turnover calculator to size correctly.

Species-appropriate husbandry: research adult size, territoriality, diet, and tankmate compatibility before purchase. Use our tank stocking calculator + compatibility guides.

Frequently asked questions

How long does an aquarium take to set up? 4-6 weeks for full cycling + first stocking. Use our cycle ETA calculator + how long does cycling take.

What's the best aquarium for beginners? 20-gallon long. Big enough for parameter stability, small enough for budget + space. See beginner picks.

How often should I do water changes? 25-30% weekly. See water change frequency Q&A + water change calculator.

Why does my fish keep dying? 5 leading causes: uncycled tank, wrong species pairings, no quarantine, undersized tank, neglected water-change schedule. See full diagnosis.