Any advice??
I've just completed building a 42000 l pond, which was filled with water yesterday. When testing the bottom drain in the settlement chamber, the flow to waste was very slow..almost a slow trickle, and the 1,1Kw Speck pump was sucking a vacuum in the pump basket chamber.
The filtration system has 4 chambers with an over-under operation. To 'dump' the water from the chambers, the pump sucks the dirty water directly to waste.
I can only assume that a piece of the concrete has been lodged in the 50mm drain pipe, somewhere between the bottom drain and the pump. The leaves have backed up against the obstruction, further restricting the flow. There are 3 bends in the pipe (2x 45 degree - closest to bottom drain, and 1x 90 in the pump room), and the length is about 7 metres.
As mentioned previously, the pipe is not totally blocked, as there is some flow, but not at the same volume as the other 3 bottom drains. Also important is that the pipe has been bedded in 200 concrete base and covered by a screed of about 30mm.
Any suggestions as to how I can dislodge or disintegrate the partial blockage, so that it can either be sucked through to the pump, or alternatively pushed back into the bottom drain area of the chamber, where the 2 45 bends are.

Sorry Jack
You can hire a plumbers steel fish to poke it from the one side. It works for a 90 bend of a 22mm electrical pipe it should work on a 50mm pipe. I hope you have used a class 12 or higher pipe, because should the pipe be thin and crashed that it will be a no go to repair. At my work place I have a crushed 110mm toilet pipe where water only trickles through.

I would push a garden hose in from the poolside ... I assume that is the easiest access to the pipe. Push the pipe until yoou hit solid resistance ... mark the pipe against the drain and pull the pipe out ... now you cam measure which end is the closest to the blockage.

Another option is to push the hosepipe in from the pump side until you hit the blockage and then open the tap wide ... the stream of water plush some nudging with the pipe could make the stuff move towards the pool.

Nudging plus the water may help wearing the edges off the concrete plug and make it move better. Be careful to not force it too hard. That might make the plug twist and lodge itself into the plastic. Small short but sharp strokes ... fairly pornographic in style may just do the trick.

The cheap stiff hosepipes is the better option ... it will be a bastard to get round the 90 degree bend but it will push better than the expensive braided type which is soft and will buckle over that distance.

I have some serious compressed air access here so I would try plan B with compressed air.

If the hoses fail ... then try to use some baling wire and push that in and try and get it past the plug and out at the other end. Now you can take a plier and twist a small piece of dishcloth onto the 90 degree en and then start pulling at the pool end Once the rag gets to the plug you might be able to drag it by giving some short sharp jerks.

Look no guarantees here but just a Boer maak 'n Plan post

So the bottom drain pipe is only 50mm and you are sucking directly from the bottom drain....and now something is blocked in the pipe somewhere...

Ouch, eina. If the waterforce of 42 000 liters of water cant push the blockage out then i dont have much hope that anything else pushed into the pipe would have any luck either.

My only advise, push something down the pipe to estimate where its blocked....and then grind the pond open to get to that section.

Thanks for the replies. Will check it out again today. As Colyn says, :'n boer moet maar 'n plan maak'. Used Class 6 pipe for the filtration, and Class 12 for pond bottom drains > to settlement.
Wayne, the settlement chamber to pump room is the problem,,,so only have 2500 l pressure from settlement chamber.
I will try the fish tape, wire, hose etc today.
As i said in my posting I believe the blockage is not solid as about 30% of water discharged flows past it until the debris//leaves build up behind it, then the flow rate decreases quite significantly.
Is there a chemical available that will weaken a concrete obstruction, making it brittle so that it will disintegrate sufficiently to pass through the system? Sounds like passing gallstones! Eina. ja.

I cleared a few blockages in the past using those "orange" polycop piping.

It can bend around 45 degree corners and can be pushed through very far with force as it does not bend easily. A hosepipe is often to soft to break a blockage or just bend in which case you can't push it in further.

You can also easily connect a high pressure water flow from the other end. (optional)

Your problem is probably at the settlement chamber bottom drain end, because that is where you worked with cement. At that end, you have 45 degree angles, so the polycop will probably go in.

You can also make the entry point of the polycop sharp to assist in breaking the blockage/pushing through a blockage and it limits the changes of getting stuck around a corner when you push it in.

Paul ... daai polycop is a baie goeie plan ... sal dit onthou.

Had exactly teh same problem, had one blocked bottom drain, the key is patience, and taking it slow, as you do not want to break the pipe.

I cleared mine with a plumbers tool, in teh following way.

They give you a spiral hook type attachment, di not use that, just took the rood and pushed it through, you should be able to do that if you have some water flow.

Once the rod was through from teh bottom drain tothe settlement chamber, attached a strong piece of nylon ski rope, and pulled that back.

Then attached a t-shirt on the one end of the rope, made sure it sits tight, not too tight to move and be pulled, and then we slowly pulled the rag / t-shirt through. Also had another rope at teh end of the t-shirt, cloth ball, so we could go back as needed. Worked 100% got 2 big blockages out that way