Backyard Aquaponics
A place to discuss aquaponics

Sumps are definately a good idea, but if you absolutely cannot have one (or dont want to do the work of digging it into the ground) then adding a float switch to your pump can save the fish.

You dont use any sort of liner in your bed? how quick do you estimate it will rot out? high nitrogen is used to rot wood quicker (for stump removal, etc)

Also, how do you stop water carrying all of the sand away during the drain cycle in an sand bed?

Well, again my Sketchup pic is a bit misleading... My plan is to lay pressure treated 2x4s along the length of the blocks (one each side) and then use a bunch of smaller cross pieces as the support under the box. So it will be strong, but I expect it to sag just a little.

Yes, I expect I'm overthinking the drainage... but since I'm awaiting the arrival of my tools (maybe tomorrow!), it keeps me occupied.

Yes (I really need to update my drawing!), I'm using a double layer of black 5 mil plastic (all I could find initially). Mark and company say that the sand really doesn't seem to move much but I'm thinking of wrapping some fine mosquito netting around my drainage pipes to help keep them unclogged.

sorry i was talking to aufin about the liner, he said he doesnt want his wood constantly wet, like it isnt lined.

a fines filter on the outlet sounds like a good idea to me, sand moves very easily with water flow, unless the drain is meant to be so slow that nothing moves (almost impossible, some will always move).

Oh yeah, I didn't notice his comment about the wood. He's got a double layer of 5 mil, according to his posts on the Aqua Nation site.

Of course I have a liner. What I was referring to is the open waterfall drain where the water just pours out of the end. I saw no good way to have the end open without everything being constantly wet. Plus it didn't make sense to me to have a waterfall, anyway. I wouldn't be able to walk around the bed without having to walk all the way around the tank, not to mention the end of the bed would be inaccessible. So far, no leaks = not rotting wood.

To keep the sand from flowing with the water I made a gravel filter with 1/8" hardware cloth for the end of the drain pipe and covered everything with a good sized mound of small pebbles to keep the sand back. Do date I have no sand that I know of in the bottom of my FT.

Allowing it to sag in the middle isn't such a good thing. Liable to pull the bottom loose from the horizontal end pieces.

I haven't watched a single YouTube video on the subject thank you very much. I'm going off the data from the iavs website on their claims that the OP sent me to not once, but twice. So I'm just suggesting if someone was going to compare the two systems it wouldn't be a fair comparison if you fed most of the nutrients to one system and starved the other system to make a claim that one was better than the other.

but that is my point, one will not starve the other because the water does not(!!) come back clean!!

the amount taken out by one bed in one cycle is absolutely minimal.

I guess that would depend on the number and types of plants that were in the bed since the uptake of available nutrients must vary significantly. But wouldn't you optimally want each cycle to take out close to the amount of daily available nutrients produced / number of cycles?

ideally it would be nice for nutrient water to flow in and pure clean water to flow out like people who dont actually understand say happens, but unfortunately it doesnt work like that.

yes different plants will uptake different amounts, but it just doesnt happen that fast, not fast enough for one bed to get lots of nutes and the next bed in line to get almost no nutes.

It would be interesting to see a graph showing how various nutrient concentrations change in the inflow versus outflow pipes over a day. I get that uptake might not happen that fast, but if the plants/bed removed, for example, 25% of the available nutrients in the intake water, why would the system not eventually contain toxic levels of nutrients?

because there are multiple passes every day, some molecules of water will pass through multiple times per hour.
as i said, it isnt all removed IN ONE PASS like people who say "water comes back clean" are insinuating.

there are systems which run at 0 nitrate, it does get removed, but rate depends on plants used / amount of beds, etc.

Well, so far I have no water flowing through my system. But I do have the beginnings of the sand box underway! It's 90 x 230 x 40 cm.

looking good!