Sump/refugium design questions (rubble vs bio-balls)

[Scoot]

Designing a sump, for my 75g, using a 20g glass tank. I want this to be both a refugium (for macro-algae to eliminate nitrate and other waste), as well as provide enough bio-filtration that I can remove my HOB bio-wheel filter.

I have about 20lbs of LR in the main tank now, adding more all the time, but I won't have the 1.0 to 1.5 pounds/gallon needed for LR filtration for some time.

In my design so far, basically there's a suspended area on one end for bio-balls or rubble, a baffle next, which overflows into the main/refugium area. The height of that baffle will depend on if I want to submerge my filter media (bioballs or rubble).

The refugium will be about 1/2rd the tank, leaving about 1/3rd for return pump and future skimmer.

I figured 2g of bio-balls would be enough for a 75g (since each g of bio-balls are supposed to handle 45 to 60 gallons).

Would LR rubble, filling the same amount of space, be as or more effective? Is it best to have rubble wet/dry/trickled, or submerged? If it should be submerged, I can turn the rubble containment area into a corner box or something.

For 2g of bio-balls, I'm allocating an area 4.5" wide x 9" tall x 12" depth, or 526 cubic inches.

If I use LR rubble, in the wet/dry section (where water trickles over) is that enough LR, or should I increase the space allocated?

Or, is LR better submerged?

I want to have a large volume for potential overflow in the event of power or pump failure. If standard operating water level in the sump is 3", that will give me about 15.4 gallons of overhead, should the pump stop returning water to the main. That's about 3" of water in my 75g, which should be very easy to work with.

With 3-5" of water in the main area, that's about 4.6 gallons contained in the sump, half of which would all be pumped to the main tank if the siphon fails. That's barely over an inch of water to the main.

So, I'd operate the tank about 1 inch below the very, very top of the tank, and never have to be concerned with overfilling the tank. With the overflow siphon in the tank setup with about 1" of water over the "spill" level, I'd never have to worry about the sump overfilling.

There'd be lots of leeway on either side. I'm not getting the benefit of adding a huge volume of water to the system (around 5 or 6 gallons total added), but it should be effective bio-filtration, a good place for a heater and skimmer, and I'd also not have to worry about flooding.

[angelscrx]

Rubble rock is way more beneficial than Bio balls. Bio balls are only useful in FO tanks but you should take them out and wash them pretty regularly. If you go with the rubble rock the cornor box wouldn't be a bad idea but i would place the rock in the the first chamber, then overflow into your refugium, then overflow to the return chamber. Just my opinion.

[Scoot]

So the rubble would be immersed, not trickled over in a wet/dry setup?

Would the equivalent of 2g of rubble be enough? Not sure what weight that'd be... maybe 8 pounds...

I'm really hoping to have something that can do both bio and mechanical filtration, and function as a fuge at the same time.

[lando]

Bio balls are only useful in FO tanks

This is not entirely true. Bioballs have been used successfully in SW for many years. However, as mentioned, they do require a bit more maintanence to reduce the accumulation of NO3. LR rubble is a better filter media in general and works a bit differently then do bioballs. Bioballs are designed to work in an aerobic environment. This is why water is trickeled over them (hence the term wet/dry). LR rubble does best in an anaerobic environment, submerged just like LR.

[ctmedman]

I'm not sure if one is more efficient than the other. I'd be curious to know the answer to that question as well. I have a tank size similar to yours (72gallon).

I bought 30lbs of rubble rock for $35 online. It's supposedly calcium carbonate and from a reef quarry bed. I can give you the info if interested. I put all of it in my sump. I think 30lbs of this stuff has more biofiltration than 30lbs of larger size rocks due to the increased surface area.

[melosu58]

As Lando stated the LR rubble needs to be submerged. I`m going to very soon be changing mine over. And yes you will need more pounds of rubble as they weigh more than the bio balls.