capacity questions

[old 5k0ol]

I have a 75 gallon FOWLR with about 90 lbs of live rock. I have an Aqua-tech 30-60(filled with bio-balls) and an aquaclear 70 filter. I'm running two hydor koralia evolution 750's. I want a pretty well populated tank when it's done. Do I have enough filtration/water flow to load this tank with fish? Any constructive advice would help, thx in advance.

[Cliff]

If you have good quality live rock, you should have good filtration

IMO, I would loose the bio-balls. If you have good live rock, they are not needed. It will only add to your weekly maintenance routine. You can use your HOBs for carbon and phosphate remover to help prevent unwanted algae

I would also add at least another powerhead. With your two HOBs and powerheads, I would estimate your total flow at 1700 gph. Personally, I would aim for around 30X flow which would be closer to 2200 GPH for your tank. This will also help to reduce deadspots in your tank and help with the bio filteration your live rock provides

[old 5k0ol]

My flow rate is actually about 2100 gph.
750 x2
aquaclear70 runs 300gph
aqua-tech30-60 runs 330 gph.

So you're saying without the bio-balls It could carry a heavy bio load?

[Surfdog]

Oldskool, I am missing something here. While The aquaclear 300/70 filters 300G per hour, the flow is only 100G per hour. As to the aqua-tech, I don't have one or ever had so know nothing of them. IMO, I believe your calculations are incorrect. The flow of my Ehiem UltraG160 rated to 160G tanks is 330GPH.

[Cliff]

My flow rate is actually about 2100 gph.
750 x2
aquaclear70 runs 300gph
aqua-tech30-60 runs 330 gph.

So you're saying without the bio-balls It could carry a heavy bio load?

At 2100, or 1700 gph, I would still add another powerhead

Also, 1 lb per gallon of quality live rock can handle a moderate to heavy stocked tank (not overstocked tho), provided you have very good flow (over 2250 min)

Just be very careful to make sure you have quality rock. There's examples in the sticky on how to cure rock.

If you have that, no need for bio balls IMO

[hockeyhead019]

Even if you have great rock I'd let everything mature and stock extremely slowly, it's not like FW where you can get away with the occasional overstocking if you have fantastic filtration. SW fish are much more terretorial and will fight to the death for food, literally they'll bully weaker fish out of food without a problem, the more fish you have + the less space you have = the more likely this will happen.

Also when you finally start to stock your tank keep in mind that you no longer have a truly 75 gallon tank! (There's a rule of thumb of so many fish per gallon of water for SW but I can't remember what it is) But anyways keep in mind that you LR takes up volume of the tank so with 90lbs of LR you're probably closer to 65 or 60 gallons of usable space for the fish... just little things to keep in mind lol

[old 5k0ol]

Thanks for all the input. I am still unsure how a filter can filter 300gph and not output those 300gph as flowing water. Is it worth it to get a HOB skimmer? Will that give me the added flow I need rather than buy a powerhead and then find that I could get the flow and benefits of a skimmer?

[Cliff]

It is certainly worth it to get a skimmer. It will help a LOT to keeping good water quality. The flow it will add to your tank will depend on the skimmer you get. Some have more than others. It will not give you the ability to give you directional flow like a powerhead will helping to reduce deadspots.

[hockeyhead019]

+1 to the skimmer idea... definitely helps keep the gunk out of your tank as things get settled in there