Confused about flow

[nickq]

Hi,

I understand I should be pushing 35gph of flow per inch of screen, however I can't achieve that since it is massive.
My scrubber has been going for 2 weeks and seems to be looking good, I'm getting green growth and phosphates are starting to drop.
However I have 2 parallel screens totalling 34 inches width, that means I need 1190gph! Or 5409 lph :o

To put that into context that means system turnover of 30x (I'm around 180L).

My sump return pump is rated 5000 Lph this is what I get out of it:
Return to display = 900 Lph
UV = 297 Lph (my UV light is turned off for pod growth)
Scubber = 720 Lph
Bypass (sump return for fine tuning) = 363 Lph

So I'm losing 2720 Lph in head losses (pipe, height etc etc).

This means I'm getting around 4.6 gph per inch in my scrubber.
If I try and increase it the drain from the scrubber starts to struggle, it is 2 22mm tank connectors feeding into 1 22mm pipe.
The final few inches of screen do not get great flow but I wasn't worried about that because this changes as the growth increases, almost like a screen overflow if you like, I'm still oversized for my tank with around 370 square inches of screen (2 screens hanging either side of lights so only lit 1 side each).

Lights are 3 23W CF 2700K.
I've also just added my old aquaray blue strips (not shown in pics below) to the non lit sides of the screens as an experiment to see if it affects that side, there isn't room in the box for more CFs. I've also now attached foil to the outside of the box to reflect light back in.

Should I be concerned and change something? Obviously I will wait and see how it matures over the next few weeks, I'm cleaning every 7 days, the growth is green slimly algae about 3mm thick.

Here are some pics before growth when new, I can add some more at the end of the week:
Spaghetti jars for keeping water away from lights and directing heat back out of the box through the open tops.
[attachment=2:1xwo9xv9]photo1.JPG[/attachment:1xwo9xv9]
[attachment=1:1xwo9xv9]photo2.JPG[/attachment:1xwo9xv9]
[attachment=0:1xwo9xv9]photo3.JPG[/attachment:1xwo9xv9]

I've removed all mechanical filtration such as floss and the return pump sponge as I would like pods for my scooter blenny.
Unfortunately I can't convince the missus to get the scubber on a shelf above the tank :|

Thanks,
Nick.

[Rumpy Pumpy]

Why do you need so much screen width for that size tank?

[nickq]

I guess I don't, according to FAQ I need 90sq inches when lit single sided.
I'd like it to tolerate a 2 week holiday so thinner growth on a larger screen is recommended for this.
I also feel good about oversizing it that my tank won't out compete :roll:

What's the ultimate question here is would a smaller screen with greater flow perform better? I would guess not in terms of nutrient removal it would just look different growing thicker algae right? Same argument as longer period between cleaning discussion is it not?

[Rumpy Pumpy]

What's the ultimate question here is would a smaller screen with greater flow perform better? I would guess not in terms of nutrient removal it would just look different growing thicker algae right? Same argument as longer period between cleaning discussion is it not?


Dunno. SMs your man to answer those.

Personally I'd either make the screen smaller (maybe two sided with light either side which, according to SMs guidelines, requires the same flow as a one sided (but you get twice the surface area) or get an auxiliary pump and plumb it to add flow by circulating some water from the sump back through your scrubber feed pipes (see no reason why all the flow has to come from the display tank as long as it's continually circulating)

[SantaMonica]

would a smaller screen with greater flow perform better?

Yes. And 2-sided.

A larger screen does nothing if not covered in flow and light.

You must have gotten your calculations wrong... 4.6 gph per inch... is barely flowing. You want the whole screen to be covered in a water fall, and in light. If you can time how long it takes the drain to fill up a gallon, you can calculate from there.

[nickq]

I measured at the scrubber outlet pipe and timed how long it took to fill a litre jug which was 5 seconds.
That's 720 Lph.
So if I divide that by my 34 inches of screen width that's 21 Lph per inch = 4.6gph/inch.

I would say 80% of the screen is covered in a solid wall of water.

I take your point on a smaller double sided screen, I'll have to pick up a new box lid on my next trip to Ikea.

Thanks,
Nick.

[SantaMonica]

1 liter in 5 seconds = 720 lph

Flow should be 60 lph per cm of slot. So if you divide 720 by 60 you get 12 cm. So your flow can only provide for 12 cm of slot (about 5 inches).

[nickq]

Ok, I guess the slot width must be why I still have a good coverage albeit thinner.
I'll see how it goes before I start hacking it all up again.
Incidentally in the last 9 days my phosphate has reduced significantly and I'm feeding more.
Using a Hanna phosphorus checker the ppb has gone from 14 to 9 which is 0.028ppm phosphate.


phosphorus ppb phosphate ppm
18/07/2011 14 0.043
19/07/2011
20/07/2011
21/07/2011
22/07/2011 14 0.043
23/07/2011
24/07/2011 13 0.040
25/07/2011
26/07/2011 9 0.028

[nickq]

I can't find the link to purchasing the SM100! Can anyone point me at it please? I'm spending far too much cash on trying different set-ups so would like to consider it. Edit: ignore me I found it after my blindness passed!

By the way, I guess the flow isn't so strict after all, I've been reading your thread on the nano scrubber which is looking really nice, but you only have 6.25 gph per inch on it.

Observing my screen this week I can see that higher flow would benefit in the sense that it wouldn't block so easily, so looks like a drain upgrade to 32mm is in order :(
I also may need to add some iron as my algae starts off green but looks more like yellow slime as time goes on.

[SantaMonica]

The nano scrubber has a totally different slot... it's just a slit that you can fit a piece of paper into. The screen does not go into it.

[nickq]

Hi, I made a few changes before anything major.
I've taken the screen out of the slot and pointed the slot at the screen, although my flow clearly isn't up to spec the water does reach the full length of the slot so the entire screen is getting flow.
The only lacking in flow is where my screen clips are blocking the slot as you can see from the streaks.
I also removed the blue leds as they were clearly pointless since I couldn't get then in the right position to amount to much.

Here are my 7 day growth pics:
I haven't cleaned yet as I may leave another 2 days what do you think?

[attachment=1:5agwt941]IMG_0068.JPG[/attachment:5agwt941]
[attachment=0:5agwt941]IMG_0069.JPG[/attachment:5agwt941]

[nickq]

As I can't make any major changes yet (due to materials and holidays) I have increased flow in the mean time by removing the end lengths of screen and joining the 2 pipe ends together.
This has reduced screen length down to 2x 10 inch single sided but increased flow to 9.5 gallons (US) per hour per inch. I know this is still low by SM standards but the screen is not in the slot and the flow over the screen looks strong and consistent all the way across.
I've also stuffed the third bulb into spaghetti jar number 1 increasing intensity on the remaining screens, so I have a total of 69W.

Another 10 days will be interesting to compare...

Bit hard to see but you should get the idea:
[attachment=0:2iyv7o0k]IMG_0075.JPG[/attachment:2iyv7o0k]

[Rumpy Pumpy]

I'd at least rinse he brown slimy stuff off