Good info already provided, but I'll try to add to it (sorry if I repeat some things)
Tips to avoid a flood:
- Use as large a sump as possible
- Keep your returns near the surface in order to reduce the amount that back-siphons when pumps are off (I would try to avoid using loc-line for your returns since you are going to be keeping big fish that can bump it lower in your water column- seems crazy, but I've heard of this happening and during a power outage, the guys sump couldn't handle the back-siphon and he had a flood on his hands- the perfect storm/murphy's law at work).
- It's a best practice to fill your tank when the pumps are not running so that you know your sump can handle the volume of water added
- Mark the maximum water level in your sump while your pumps are running so that you know how high you can fill without risking a flood. This helps in case you ever "top-off" your tank while the pumps are running.
- Make sure your design is such that if your mechanical media becomes clogged, the water can bypass the media and continue to flow through your sump. A rookie mistake is hanging filter socks in such a way that when they become clogged, they overflow out of your sump and onto your floor.
Other tips:
- Use large plumbing- it helps reduce friction loss in your return lines and gives you the flexibility of running more GPH if you decide you want increase turnover (see below for a good chart and recommended pipe size taken from Reeflos website).
- Use efficient pumps. Lagunas, Reeflo, and the new DC pumps are efficient and will save you a lot of cash over time. Pumps to avoid (IMO) are Mag Drives, Iwakis and Blueline. There is no need to run a high pressure pump that consumes a ton electricity for a standard below the stand sump with less than 6' or 7' of head.
- Not necessarily sump related, but look into buying Seachem Safe to condition your water for water changes. It is the dry/powder form of Seachem Prime, but it is super concentrated (1KG costs only ~$30 and treats up to 200,000G) so it will last you a long time and save you a lot of cash over purcahsing liquid conditioners.
- If the tank is 8x2x2, the aro will likely outgrow it, but that's just another excuse to get an even larger tank. =)
Regardless of your filtration (unless you have a ton of plants) the best practice for keeping your stock healthy is consistent frequent water changes.
Learn from the mistakes of others. You can never live long enough to make them all yourself.
