Advice On Debris; Do I Need A Filter Upgrade, Alter Flow Rates Or Just Feed Less

Hi,
I have a love fish 64L tank currently running with the internal filter that came with it. I have 9 penguin tetras. Its not a planted tank, but I have 2 java ferns, 2 anubias and hornwort floating. Its a relatively new tank, I moved the fish in at the beginning of Feb once the tank was fully cycled after doing a fishless cycle (from Dec-Feb). Its been running fine with ammonia and nitrites always zero.

I've been doing at least weekly water changes for the last month, initially I was doing them more frequently, as I'm finding I'm getting a lot of debris on the sand at the bottom of the tank and the water starts to turn brownish/green within the week. I suspect I'm over feeding, I definitely was initially, but I've tried to reign it in a bit. I'm feeding flaked food. I tried frozen bloodworms, the fish mostly ignored them and they just sank to the bottom!  (I tried different ways of feeding them to the fish, but it just seems they werent keen on them). They love the flaked food, when I put a pinch it theres a feeding frenzy - but once it falls more than 3 inches from the water surface they ignore it and it falls to the bottom. I am just giving a small pinch once a day to them, but I'm still finding a lot falls to the bottom through the feeding frenzy.

I am wondering is this just a feeding issue? (advice please, if so!!)
Or maybe if I had a better flow rate and/or filter would less fall to the bottom and maybe more would get sucked up and dealt with in the filter
Do I need to look at my circulation/dead zones, again to possibly move more of the debris into the filter? 
I'm wanting to upgrade my filter anyway I think, as apparently the internal ones arent very good, but at the moment mine does seem to be OK in terms of water chemistry - its really just the debris/look of the tank that seems to be affected.

It would be great if I could get the tank needing a less intensive maintenance schedule, the hoovering and water changes have got to be stressful on the fish to a certain degree (they certainly dart about when it happens anyway).

Thanks in advance for any advice!!!

Its a bit of a shame the big stuff just drops (!) We need robot vacuums for the bottom of our tanks!

Yes, I get the impression the filter is the minimum option. Its didnt have a name/manufacturer - just came with the tank from LoveFish - its got a white sponge matt and a coarser green sponge matt and sits inside at the back of the tank - so not much to speak of. I was thinking of saving up for a Fluval 106 canister, or similar, but I was a bit worried that it might be more filter than my tank needs and the flow rate will blow my fish all over the tank.

I ended up with more of the (fake) penguin tetras than I originally planned for as some of my original shoal died/disappeared and the rest started really turning on each other - after fearing they'd all eat each other I went and got more to try and even out the pack (which thankfully worked!). In my ignorance I assumed I'd loose more when I bought/introduced more, but all survived and seem to be thriving  But its got me worried that I'm expecting a lot from a smallish tank with the 9 I have left - which is why I wondered if a better filter might be a good idea.

I'd love to go for some shrimp - I'm a bit worried that they will be eaten! But just picking big ones is a good idea.     

Ow, thanks! Thats reassuring. I was nearby Pets at Home today so I popped in to have a look at the amano shrimp. I might give it a go this weekend. Thanks!

Filters that come as part of a kit are usually overpowered for the tank size.  That's not the case here though.  The filter that's in the Love Fish 64 l set is basically a Interpet CF1 filter that isn't very good that's recommended for a 36-68 l aquarium.  As Sue says the filter itself won't clean the mess off the sand but a new one will address the flow rate concerns you have.  If you do get a new one (and for your peace of mind I would) don't forget to put the old filter material into the new filter when swapping over.

The brownish/green water is likely to be an algae blown as the tank is full of nutrients.  Amano shrimp are really interesting.  I have some in two tanks now.  They'd definitely eat the larger bits and are great cleaners.  If you're not adverse to snails I would also recommend Malayasian Trumpet Snails as an option as they will churn the sand for you.