I've kept large tanks from 180 to a 700 gallon (9x3x2.5 feet) beast.
1. After weight, your first consideration needs to be ease of access. Make sure that you don't get dimensions that you're not going to be able to reach all areas of. For me, this is approximately 24" tall by 30" front to back if I get in up to my armpit. Seriously, you do NOT want a tank that you can't
easily reach every single corner, crevice, and nook of, no matter how good/impressive other dimensions may be to you. The harder it is to maintain, the less you'll do it, and in a big tank a lot of crap can build up.
Make sure to account for a canopy as well. It doesn't help to have tank dimensions you can get to if the canopy prevents you from accessing where you need to go.
2. Filtration- If you get a sump, be Real
[email protected] Sure it'll be big enough to hold the water you're going to need to both run it and hold the water that drains from the tank when the pump's off. I've encountered systems that can't stop the pump because a) the sump will overflow and b) the sump runs dry before re-filling the tank when the pump's off. Big tanks need a lot of media; when designing your sump I'd make sure there's room for at least a 5 gallon bucket full of media such as Matrix.
Forget filter socks, they'll need to be changed a couple times a week and that gets annoying AF. (again, easier maintenance = more consistent maintenance)
Get the biggest sump you possibly can and make sure it's got a large reservoir section. Big tanks evaporate a lot so you'll need an equally large reservoir to compensate.
Auto Top Off systems are nice but
will fail and overfill at some point. It's inevitable. A handy option would be to have a spigot that you can use to directly fill the sump as needed. A long hose hooked up to a sink also works well.
3. Circulation- If you're going Penninsula style, make sure your pump's strong enough to circulate that amount of water across the entire length of the tank by at least 3 times; across the top, across the bottom, and enough extra to keep debris moving into the overflow. Anything less than this will increase your maintenance load quite a bit since you'll have to vacuum the substrate more thoroughly than you would otherwise have to.
DC, pressure rated, pumps. Don't consider using anything less.
4. The Overflow- I'd STRONGLY suggest investing in a tank that has a Coast-to-Coast overflow; ie, one that will go across the entire side of the tank that's got your drains in it. Big tanks produce a lot of leaf litter that loves, loves, loves to block overflow teeth. The larger your overflow area, the less likely it is to get clogged and cause a flood (always when you're not around to handle it right away).
5. Don't get one of those hang on the back style overflows. I loved mine on my 80 gallon, but it got clogged one night and my downstairs neighbor banged on my door at 11 o'clock..... DRILL THE TANK. Since it's going to be a room divider, drill the bottom and have the overflow be a second pane on that side. This will allow you to have a straight drop to drain into the sump and will hide the drains.
6. Don't silicone your drains into the bulkheads; you'll want to be able to pull them out to flush collected debris (and animals) into the filter.
7. Herbie/Full Siphon drain design is your best friend. Big drain pipes make big noise.
8. Don't plant a massive foreground of carpeting plants. Trimming square feet worth of something like HC or Monte Carlo is the path to insanity. A sand foreground is your best friend.
9. Lighting- If you're doing the peninsula thing, high-power LEDs will actually work well since they'll be running down the center of the tank and you won't need a lot of PAR for a massive carpet. Seriously. Don't plant a carpet. Trust me. T-5s are another strong option and can look very good if you get a good unit and suspend it from the ceiling.
10. Get a siphon hose long enough to drain to a tub and the connections needed to hook directly to a sink. This will make water changes much easier.
The 3 most important things-
1. Plan, plan, plan, plan, plan, and over engineer, over engineer, over engineer. True Union gate (not ball) valves are going to be your best friend. Make everything modular for easy removal and maintenance. Check out the large tank sections of reef forums for builds. They're still the experts in this area.
2. Don't cheap out. Seriously. Buy the very best you can from the very start. Big tank hardware is expensive and it'll be cheaper in the long run to fork out the money once rather than having to replace something that broke/wore out/wasn't sufficient to begin with.
3. If you can, rig up an emergency drain in your sump just in case. Replacing a burnt out pump is cheaper than replacing flooring and/or having to pay someone to come deal with water damage in the walls.
I hope this helps and I'll be more than happy to answer other questions that arise.
Phil
