Backyard Aquaponics
A place to discuss aquaponics

Yeah I have pages from Global Plastic Sheeting's Ultra Skrim in tabs right after my Americover Dura Skrim pages. I'd be temped by Ultra Skrim if for no other reason than just for the shipping weight. Supposedly its 1/2 the weight of Dura Skrim. Shipping weight for 6 ft x 100 ft Dura Skrim is 69 lbs. The Ultra Skrim comes in a slightly wider roll which could provide for a slightly better overlap (6 ft 2 in vs 6 ft). The Ultra Skrim is slightly more expensive for a 100 ft roll ($255 vs $216 USD) but Global will ship it for free to Florida (maybe the US48?) and Americover will charge $67 USD. That makes the Ultra Skrim cheaper.

I'm skeptical about one Global's claim that Dura Skrim is not food safe. TCLynx used it and also said that she knows of organically certified farms that use it. Americover's Dura Skrim description says...

20 mil Reinforced White R20WW by Dura Skrim®

BYAP thread: Food Safe Liner

I haven't figured out what Import Tax would be on a 100 ft roll, but I think I'll chat with the freight forwarder and ask.

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Sam

Thanks Sam, good to know re Dura Skrim. I'll be very interested to hear what you find out about shipping!

Update time! Yesterday was sand day and today I finally got some water running through my system. Everything seems to be working well so far. The contractor's sand I found is a bit coarse (see photo) but drains well. I had to wash it (a task I recommend to avoid!) and there was some residual silt in the initial flow of water (see photos of cups showing initial water and after 30 minutes of flow) but it's running clear now.

That is excellent progress!

Do you have a feel yet for how much water-flow you can get through the sand? I need to go back and reread the iAV docs, but I was wondering if you have to throttle it back a bit on the water inlet to give it enough time to pass through the growbed? Maybe it is just in my head that water-flow in a sand bed would be much slower than a gravel bed?

Your prototype is looking interesting!

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Sam

Hi Sam,

Yeah, I think I might be running the water a bit too fast. The iAVs docs say:

Irrigation Intervals and Volumes
What worked best for Mark was to move approximately 1/4 of the tank volume (drawn from the bottom of the tank) – 8 times per day at 2 hour intervals. This provides two complete tank volume exchanges daily.
The drainage cycle is such that water begins to drain from the bed well before the end of the flood cycle. This means that fluctuations in the fish tank level are quite modest. Depending on your sand bed pore volume (relative to fish tank volume), the water level in the tank will drop by about 10% … more or less.
The number of events per day will depend on your latitude and the season.
Schedule the first daily irrigation event to begin at dawn and begin the last event of each day so the sand bed drains before dark.

(http://iavs.info/backyard/sand-bio-filt ... on-part-2/)

And from the previous page (http://iavs.info/how-to/sand-bio-filter ... on-part-1/):

Mark typically featured a flood duration of 15 – 20 minutes and a drain cycle (OFF time) of around 100 minutes.

So basically, I should be moving around 1/4 of my fish tank volume in about 15 minutes. My current pump (rated 4000L/hr) is doing quite a bit more - haven't calculated exactly based on the height of my grow bed but will check some more tomorrow. If I keep the IBC about half full (500L) then I should be able to get away with a 500L/hour pump - at about 1 meter of head.

I think my sand is a bit too coarse and am a bit worried that the water will drain through too quickly because of the pore volume. In these first few floods, the furrows certainly didn't completely flood. But I imagine after some debris has accumulated on the surface, the flow should be more evenly distributed. I suppose if I hadn't have washed it, the finer particles might have slowed things down more. Sigh.

Anyway, it's certainly fun to at least have something that -might- work!

crushed river rock is a bit of a stretch to be called sand in my book... not that my book really matters, just doesn't seem to be the model of what iAVs claims are based on.

Yeah, I think you are probably right. Perhaps I'm operating in "no man's land" between sand and gravel. Here in Costa Rica they don't call it arena (sand) either. It's known as "pulvo de piedra", or crushed rock basically.

Well, if nothing else, my system can serve as an example of what happens when you go to a 3-4 mm size granule!

Day two of adding water. Got the timer going and for the next few days, will have the pump on for 15 minutes then off for 45 throughout the whole 24 hours. Then I'll dial it back to 15-20 minutes 8 times a day with 100-105 minutes in between each flood (120 minute cycles).

The water is making it about half way down the bed today. I expect it to make it all the way in a few days after the furrows develop some surface matter.

looking forward to seeing this thing run 24/7 and get some plants in it!

Nice endeavor in no mans land. I still get a kick out of transparent aluminum. I need to go back more than a few apages which I just now did to see how you got started with this setup. looks great at this point.

Great job

Inviato dal mio ALE-L02 utilizzando Tapatalk

Thanks all. I forgot to mention that I also installed a bottom drain using a bulkhead fitting to make sure that the bottom of the bed has as little standing water as possible. There was about an inch or so of water remaining before because my main drain sits up off the floor a bit. Next time I'll just run the main drain out the bottom.

All these close ups made me feel like I should post something a little more scenic to show you were we are located. Heredia, Costa Rica is a beautiful mountainous location and our rental property has a great view out the back towards two volcanoes: Irazu, that mountain in the background, and just off to the left of it you can see the plumes of smoke and ash coming from Turrialba, which has been quite active recently. Fortunately, most days the ash is blowing in another direction!

My return water is coming out much clearer now than than first picture, which was taken soon after I first added water to the system (so there was a bit of left over silt running through the drain). I also added some urea so will check the ammonia and nitrate levels in a few more days.

It's not necessary to completely empty the bed. Because it's so shallow it's already well oxygenated but by draining from the very bottom you'll be removing some solids back to the fish tank (it's better if they mineralize in the grow bed). Don't be concerned about what you've already changed but don't waste your time with this it shouldn't matter. On the other hand if the surface stays moist when it doesn't drain fully because of the fine media you may be right to do this (algae might become a problem).

On another note - The clear tubing will grow algae if left exposed to sunlight so you might want to change that