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Setting up a new 75-gallon mixed reef tank and debating sump size. I've heard conflicting advice on whether a 20-gallon or 30-gallon sump is better. What's your experience with sump sizing for coral-heavy systems? Running a protein skimmer, chaeto, and some media reactors.

I'd go with the 30-gallon sump, no question. More water volume means more stability, and you'll appreciate the extra space for equipment. My 80-gallon runs a 40-gallon sump, and it's been a game-changer for keeping params steady, especially with SPS.

Agree with dorvik. Larger sumps buffer against parameter swings. My 60-gallon tank has a 25-gallon sump, and I've never had issues with alkalinity drops. Just make sure your return pump can handle the head pressure.

Is there a downside to going too big? I've got a 50-gallon sump on my 90-gallon tank, and it feels like overkill. Maybe I'm just wasting salt mix.

axonix9 wrote: ↑Sat Sep 06, 2025 12:05 am Is there a downside to going too big? I've got a 50-gallon sump on my 90-gallon tank, and it feels like overkill. Maybe I'm just wasting salt mix.

Nah, bigger is always better if you've got the space. More water volume dilutes nutrients and gives you wiggle room for errors. My 100-gallon display runs a 55-gallon sump, and it's chill.

The key is balancing sump size with your equipment needs. A 30-gallon sump for a 75-gallon tank is solid, but ensure you've got enough room for your skimmer, reactors, and maybe a fuge. My setup's similar, and I've never regretted the extra gallons.

I'm in the same boat as OP. Debating between 20 and 30 for my 65-gallon. Leaning toward 30 after reading these replies. Anyone running a refugium in theirs?

leanmax wrote: ↑Sat Sep 06, 2025 9:04 am I'm in the same boat as OP. Debating between 20 and 30 for my 65-gallon. Leaning toward 30 after reading these replies. Anyone running a refugium in theirs?

Yep, I've got a chaeto section in my 35-gallon sump. Works great for nutrient control, but you'll need a light. I use a cheap LED clip-on, and it's been fine.

Thanks for the input, everyone. Sounds like the 30-gallon is the way to go. Appreciate the advice on the refugium too.

One last tip: if you're doing a fuge, keep the flow low. Chaeto likes a gentle tumble, not a whirlpool. My first setup looked like a blender, and the chaeto hated it.