Crud Build Up On Sand

Hey everyone

A week and a half ago I changed the gravel substrate in my 40L, Aquastart 340 pro fish tank to sand. I found and bought this awesome fine black aquarium sand from trademe. I had no issues cleaning it, and bought black sand as I thought that perhaps I wouldnt be able to see the fish waste as easily(compared to white sand). The build-up shown in the pictures is after just 2 days. I have been doing partial water changes everyday with a siphon, removing about 3-5L each time to try and keep my tank looking clean but I havnt got time to do that every day Any ideas? I have supplyed pictures(sorry about crud quality)so you can see how it is set up and the position of the filter inlet. Since the filter is a top external filter kinda thing I can't change the position of the inlet. I have tried moving the decorations around to ensure better water flow but its not really helping. In the last photo you can see the poor water quality with particles everywhere, even though I have tried all sorts of clearing products. I never have had problems with quality in this tank before.

I have a 75 L tank also which has a coarser type sand, does the coarseness make a differance? There are a few since as its my fry rearing tank but I never had this issue with gravel, my water quality was much better with the gravel also? I had an idea of mixing the sand from the two tanks together then putting it back, but as my bigger tank has a lighter, heavier sand I dont want to risk it and end up with crappy sand at both ends haha.

Any help would be appreciated.

Try repositioning the lump of timber a bit so that it helps make the gunk flow towards the filter pick up, also sloping the sand down towards that point will help it make its way there. Any time I get gunk accumilating in a pocket I just put my hand in the tank and wave my hand towards the filter and it gets the stuff off the bottom and then it can get into the inwards flow of water going into the filter. Also my cory's do a pretty darn good job of keeping stuff moving in the tank.

Potentially obvious solution but have you tried feeding less? What goes in must come out. I don't even feed my fish every day.

You could also try adding either a power head (though your tank is a bit small for that), or, which I have done before, add a small internal filter right at the bottom, on its side, so it adds more of a current to the bottom.

Sufficient flow and reduced feeding keeps the waste from building up so quickly.

I have two pygmy corys in this tank, but they seem to little to move much around, I have 6 more ordered for mid january which may make more of a differance. They also seem to spend more time swimming mid level then on the bottom. I'll certainly try sloping the sand down toward the back of the filter, bit concerned about it looking weird though? Ive seen tanks with the sand at its highest point at the back of the tank, lowest at the front to create depth? There are two chunks of wood in there, I may take one out to make it easier to reposition the wood, however I have 19 baby bristlenoses in their and dont want to remove too much of their food sources lol. Once they are a little bit bigger I'll move them back to my big tank though.

Soybean: These guys only get fed once a day, and not alot either. Im already a bit concerned about not feeding enough with them being fry and all. I dont want to slow their growth down anymore then it already has been by being in a small tank Is there perhaps a better type of food I could feed that you feed less of? They get nutrafin max colour enhancing flake crushed finely, and the bristlenoses get algae wafers or spirulina. They are still too little for bloodworms and I have had issues with frozen daphnia and brineshrimp making a heck of a mess before. What do you feed your fish? I suppose the colour enhancing flake could be causeing brighter coloured poop as it is a brightly coloured food?
I have got a small filter which can be used in a ten litre tank, its low voltage and not very strong, but I could give that a go in there

Thanks for your fast advice guys