Backyard Aquaponics
A place to discuss aquaponics

There are many BYAP GB's out there now and are more and more being sold/bought second hand, consequently I occasionally get questions from customers regarding them, ie: how many bags of clay do I need?... or what siphon standpipe diameter is best suited?... So I'm curious as to the actual gravel volume they will hold if filled to their maximum practical level, ie: a cm or two from the top, I've been told everywhere from 600L to 800L by customers.

Also, what sort of F&D cycle times those with siphons are getting for different sized standpipe diameters. I've always thought the GB volume was 600L so I've been recommending 25mm or 32mm, with most going 25mm. The feedback I've got on F&D cycle times for 25mm has ranged everywhere from 10 min's to 28 min's... In theory there shouldn't be such a big variance and I'm wondering what the ball-park is for those using them.

The BYAP growbeds are 500L volume and come with 25mm standpipes.

The drain time will depend on the size of the holes in the base of the standpipe. You can adjust these by drilling different sized holes and twisting the pipe to align with a different sized hole. Generally mine drain in about 30mins hence why I run my timer 30m on 30m off.


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I think you will find the exact volume of the BYAP GB is larger than 500L (I've never bothered to measure it precisely) I've got "500L" of media in mine and there is still some freeboard.

I've got a 40mm drain, but I am using a 25mm standpipe (at the moment -- I tinker) I have a 6mm slow-drain hole and the GB drains under gravity in about 30 minutes, I run 15/45.

If you're going to play with siphons: they are dependent on the volumes of water being moved in a particular time period. Common siphon problems generally stem from insufficient flow to start the siphon, to too much flow wont allow the siphon to break. Other problems can occur when a siphon can be "starved" when not enough water can move through the media and/or media guard when pumping harder will only lead to an overflow and reducing the flow means the siphon wont start, and sucking the water hard through the media means it is not well filtered. Standpipes and timers are often a simpler solution; don't get me wrong though, there are some systems where they are required, but I've seen too many people use them "just because" or because they're "cool" without actually needing them.

Thank for the input guys, but I don't want to start another Siphoned v's timed debate.

Long story short, I've had a few customers buy siphon kits off me to run in the BYAP GB's and they've quoted F&D cycle times from 28 minutes, all the way down to 10 minutes. After experimenting with different siphon standpipe sizes in various GB capacities over the years I thought I had a pretty good handle on it and could roughly estimate the F&D cycle times with various combinations of standpipe diameter and GB volume... but the 10 min F&D cycles I find very hard to believe, and at the other end of the scale 28 min's is really getting up there, and not really ideal for FT turnover etc.

I really just wanted to find out the GB capacity, roughly, and get a ball park on the timing of siphoned F&D systems running 25mm standpipes in the BYAP GB's, and possibly 32mm... Cheers!

Just don't forget that you aim to turn over your FT volume at least once in that hour......