Thanks for the feedback.

I was thinking of putting the straws in vertically from wall to wall so
the water can't go around. I'd hold them off the bottom using light
diffusers and plastic window screen fabric. If the straws float I'd put
the same thing on top. My filter runs top down but because of the piping
the tank stays full of water, so I'd just pore the water in the top. I
was worried about how to distribute the water (so it all doesn't go
through just a few straws) but the fact that there's resistance to water
going through straws would help distribute it.

I'll go buy a box of straws and try this out in my sink.

Your point about water resistance is why I'm looking into this in the
first place. What I have now is a bunch of bean bags made from screening
material and either pea gravel or plastic beads (same as beenie baby
beads but I have 100 lbs). It's really easy to work with so that part is
good. I have them stacked up in a wall and made a horizontal flow
filter. Even with a prefilter of nylon batting the water doesn't flow
through very well. There's probably a 5-6" difference in water level
between the input and the output. I've looked at the bags and they don't
seem to be plugged so I don't know what's going on. I do have a pond
full of green algae (soup style) but I don't see any gunk in the bean
bags. What I'm afraid of is the bean bags provide enough drag on the
water that most of the water is going between the bags. I figure straws
would have much less resistance.

Matt


Snooze wrote:

The math on the surface area of a straw seems correct. However you need to
remember straws are really tiny pipes, even when under pressure, the flow
rate of water through a straw is horrible. The water is much more likely to
go around the straws, compared to the water that will flow through the
straws.

I suppose that if you placed the straws vertically, and forced the water to
travel down a bed of straws, it would work. But if they were laid
horizontally, and the water just flowed around in a stock tank, very little
would actually flow through the straws.

Sameer