Yet another flow question...Please advise

[jgr]

I am in the process of setting up a 75g reef tank. I currently have 3 Maxi-Jet 1200s (300 GPH), an overflow that is rated at 800 GPH, and a sump that will probably hold around 20 gallons. I'm guessing that the total system size will be 85 gallons.

Other posts suggest that I should be moving 10 - 20 times the amount of water in the tank per hour. That would translate to 850 - 1700 GPH.

My principal question is what pump would you suggest? I had been planning on either a Mag 7 (450 GPH @ 4') or a Via Aqua 3600 (600 GPH @ 4'). With the Maxi-Jets, this would give me either 1350 or 1500 GPH. But then I went to visit my LFS and he suggested that I get a Mag 3.5 or Mag 5. I told him that this seemed a little too low, but he claimed that with the 3 Maxi-Jets, any more than the Mag 5 would make the tank too turbulent for clams, soft corals, etc and that I might also run into a problem with small bubbles.

So, here are my other questions:
1. Are his points valid? My impression is that they are not.
2. If they are not, will either the Mag 7 or the Via Aqua 3600 be sufficient? Or would you suggest another pump?
3. If I use the Mag/Via Aqua, will a single outlet for the return from the sump be sufficient, or should I have two outlets to reduce the force of the outcoming water?

Thanks so much for the help. This forum is a fantastic resource.

 

[Brenden]

If you plan on having a FO tank then 10x will be enough. If you want corals in the future you need 15-20x flow. If your overflow is rated at 800GPH you need to get a pump to match it, probably around a mag 9.5 if that is the brand you want. You can put a ball valve on your return line to keep your tank water level at the correct level. I would split the return line to have two outputs. Get some loc-line for your return line so you can put the current where you want it easily.
To answer your other question. No your tank would not be too turbulent for clams or corals. Sounds like you are better informed than your LFS.

 

[dskidmore]

No point in getting a bigger pump and throttling it back. Same effect as weaker pump for more money.

You don't want the flow through the sump to be a torrent, go with the lower sump pump, and more in-tank circulation.

Dividing the outputs is a good idea. If you put 100% of the return in one place, the LFS guy would have a point, but if you spread it around, then everyone gets a little current.

 

[Brenden]

If his overflow is rated at 800 gph it would not be throttled back. If you take a mag 9.5 and figure in head pressure plus bends and resistance in the return line it will match up almost perfect. If you put a small return pump in the sump the water level in his main will stay low unless he throttles back his overflow. A mag 9.5 is only $10-15 more than a mag 7. This is cheaper and less of a clutter than adding another PH. You want good flow through your sump since heaters skimmer etc will be there. More flow through the sump = more in-tank circulation. Did I miss something?

 

[dskidmore]

You can put a ball valve on your return line to keep your tank water level at the correct level.

Sounds like throttling to me. Your pump may be rated for 800 GPH, but you won't get it with a ball valve on the return line. You'd then have to calculate actual GPH by timing a bucket filling from the drain line. (Drain line GPH should always equal return line GPH.) You'd then be a bit short on your total GPH goal anyway.

You could consider a HOB closed loop if you don't like powerheads in the aquarium.

 

[tecwzrd]

Most overflows either in tank or hob are adjustable to keep the water level where you want it no matter what pump you use. I’d also go with the larger pump myself and throttle it back if needed since the Mag pumps in particular are less sensitive to back pressure than other pumps. Having more flow through the sump and having less power heads in the tank is always more aesthetically pleasing IMO. That and if you upgrade to a larger tank down the road you won’t have yet another upgrade to buy for it.

Edit: I did forget to mention that too much flow through the sump can be bad if you have a in sump skimmer though but we are only talking about 800 gph and not 1500+gph so it’s not an issue in this case.

 

[dskidmore]

Edit: I did forget to mention that too much flow through the sump can be bad if you have a in sump skimmer though but we are only talking about 800 gph and not 1500+gph so it’s not an issue in this case.

Doesn't that depend on the volume of the sump?

 

[tecwzrd]

Somewhat, his is a 20 gal sump probably holding around 13 gal so 800 gph should be ok. Most sumps are 20 to 50 gal for most tanks (Brenden excluded ) and if you are rushing 1500+ gph of water by (which I have seen some do) then so much is bypassing the skimmer that it has a harder time doing it’s job. You also have to consider that most skimmers are in just a small section of the sump and not in the main part.

 

[jgr]

Great. Thanks for all the advice. I think I'll go ahead and get the Mag 9.5 and throttle it back if necessary.