Flow - low, medium, high?

[todd141]

Had my tank for about 7 - 8 months now, and am completely confused when I read a certain coral requires "medium" flow or "high" flow...

What does this really mean?

What is Low versus Medium versus High? I can imagine what High Flow is, but what is the "minimum" for low flow?

My current equipment is (75 gallon tank) a fluval 405 (carbon and some filter floss only -and the floss is changed every 3 - 4 days) an Octopus BH300F and an aquafuge2 with Chaeto and more live rock. Display has about 100 lbs of live sand and about 90 - 100 lbs of live rock.

I have 2 Koralia 3s in addition to the fluval's return ( which is about 200 - 300 gph.)

The koralias are at opposite ends pointed towards each other, and that seems to be working well. I have a third koralia 3 and when i put it into the tank i get sand moved around (tried ALL kinds of positions for the third K3) and it just seems like too much. No SPS, just a couple of LPS and zoas and leathers.

Do I need to put the third K3 back in? I'm finding it almost impossible to eliminate ALL dead spots - there seems like there will always be a few. I will feed some cyclopeeze and watch how the flow goes - it seems to be moving around almost everywhere.

Is my flow enough with just the 2 K3s?

Thank you in advance for any comments/recommendations/advice for this newbie.

 

[Stanley-Reefer]

I think the Koralias are good. I have 2 3's in my 90, but the downfall is your turnover pump in your canister of 2-300gph. You might be better off doing a sump and good return pump with around 800-100gph.

 

[KarlBob]

I think you're right. No matter how you place the powerheads, as long as the tank contains irregular shapes like live rock, there will always be a few dead spots here and there. The main goal is to keep them as few and as small as possible. A good secondary goal is to make sure you can reach the remaining dead spots with a turkey baster or similar implement, to periodically stir up any detritus.

I think the definitions of high/medium/low flow will always be subjective. Very few corals like to be directly in the path of a pump like a Maxi-Jet, with very strong laminar flow. Some corals can tolerate being directly in the path of a propeller-style powerhead like a Koralia, because the flow is more turbulent. Of course, distance makes a difference, too. A coral "directly in the path" of a powerhead three feet away receives much less flow than a coral "directly in the path" of a powerhead six inches away.

One way to visualize flow is to look at something "wavy", like a xenia or a frogspawn. If the polyps are pointed straight downstream, and "flapping" rather than waving, that's pretty high flow. If they're gently waving, that's medium to low flow. If their movement is barely detectable, it's very low flow (maybe too low). Ultimately, unless you can submerge some sort of flow meter (and have a chart to compare your readings to), you'll have to do some guesswork and trial-and-error placement to find the best spots for your corals.