Only front of acrylic tank getting dirty?

[All-in Salt Tank]

Hello!

I haven't been on here in a while. My tank is doing great overall but curious about why the front of my tank is getting so dirty while sides and back are not.

My system is not typical and I'm trying to keep it as simple as possible...

Running:
- Two Fluval FX6 canister filters both returns pointing towards front (maybe causing issue?)
- Protein skimmer
- Two wave-makers (from right and left sides)

I'm stocked with:

- Large blue hippo tang
- Large yellow tang
- Med/large dogface puffer
- Med fairytale wrasse
- Med coral beauty
- Sm/Med striped damsel
- Urchins X 2 (one is a pencil urchin)
- Few turbo snails
- Med chocolate chip starfish

Pics show from side and front. Tried to get pics of most of my friends. So hard to get them all in one pic!

 

[mann1139]

It looks like your lights might be slightly offset, and more light is hitting the front than the back.