Backyard Aquaponics
A place to discuss aquaponics

Yeah sure, you can just raise your grow beds even higher and bury your fish tank just a little. As long as your grow beds are higher than the fish tank you can pump up to your grow beds and let gravity drain the water straight back to the fish tank.

Bear in mind that this method reduces the amount of grow bed space volume you can have because you can only pump a certain amount of water out of the fish tank before the fish become unhappy. You can get around this problem and have more grow beds if you fill them sequentially using an indexing valve i.e. only fill one bed at a time thus reducing the amount of water that is out of the fish tank at any one time.

You could have an above ground sump and run two pumps as well. The sump then basically sits just below the level of the grow beds and has a pump that has a float valve. Once the water gets to a certain height it kicks of the float valve and returns the water back to the fish tank.

Edit: Yep, like the BYAP systems

Lots of options, all have their pluses and minuses. Personally I like digging big holes

If you started with all of your grow beds full of water and the sump full of water and do a continueous flow system, then sure the small sump could work. But what do you do when your plants start to transpirate and your sump slowly get less and less water in it.You see no matter how you configure things you have to think about how much water your grow beds will hold in total and therefore how much water you need to have on hand to pump into them.

If they are all full at the same time, the lowest water holding vessel in your system (fish tank or sump) has to have enough capacity to cater for all your grow beds now and into the future if you expand; plus some extra to give the system some redundancy

I know you don't want to dig too far and a half IBC would only need a small amount of digging but, if you have any way of putting your grow beds higher than the 1000 litre tank wthout cutting it then I would. That is just me, I hate cutting down a perfectly good and sound IBC

Even if you only half bury it so that it is only 10 cm or so lower than the bottom your grow beds you can a least use gravity to get the water back to the fish tank.

Later if you decide to go CHIFT PIST then you use the half buried tank as your sump and put another tank in so it is above the level of your grow beds.

4000 litre pump is fine, mine is 6000lph, but at the 1.8 metres of head I have it pumps about 2000lph.

Yes you would have less airation and it really depends on how many fish you have in your fish tank, but with any timer based system it is a good idea to have air running as well. If it is battery backed up air then all the better.