Okay, it sounds like the cloudiness may already be improving a bit on its own. The reason the aquarium no longer looks cloudy when you view it from the front is that the aquarium is longer than its wide, so when you look at it from the front, you’re looking through a smaller volume of water and there isn’t enough fine suspended matter in that shorter distance from front to back to make a big difference. But when you look at the aquarium from the end, and you are looking through the entire length of the tank, there are enough suspended particles to make the tank appear cloudy. That’s not uncommon with the tank that has just been set up, and I wouldn’t be too concerned about a small degree of cloudiness at this point. That’s a fairly common phenomena with new aquariums that haven’t yet cycled.
I would go ahead and add your live sand and precycled rockwork to the tank at this point. It may make the aquarium even more cloudy momentarily, since some fine sediments are bound to be released in stirred up from the gravel and rock, but it will be very good for your tank in the long run. You want to add the live sand and precycled live rock straightaway because the beneficial bacteria contained contained within the live sand and the precycled rock will greatly accelerate the cycling process and provide the aquarium with some instant biological filtration ability. Just make sure that your aquarium doesn’t overflow when you add the precycled rock and the substrate. You’ll have to turn off the pumps and filters temporarily, remove some of the salt water from the aquarium (a volume of water that’s approximately equal to the amount of water the substrate and rocks will displace), and then add the live sand or substrate, positioning the rockwork to form attractive arrangements that are securely anchored by the way they fit together, rather than feeling rickety or at risk of collapse. You could also add any artificial decorations at this time as well.
Once the sand, rockwork, and decorations are in place, top off the tank with some of the saltwater you removed to adjust the water level to the proper point, and then restart the pumps and filters. Don’t be alarmed if the aquarium turns a bit murky or cloudy when the live sand or substrate is added. It’s normal for some fine sediments and particulate matter to be stirred up and released when you’re adding the rockwork and live sand, but the aquarium should clear gradually over the next several days all on its own as these particles settle out or are removed by the mechanical filtration in the aquarium.
At this point, I should also mention that your Polyfilter Pad is designed for chemical filtration, not mechanical filtration. The Polyfilter Pads by Poly-Bio Marine Inc. are wonderful for a saltwater aquarium that has completed the cycling process, but they are counterproductive in the newly set up aquarium that has not yet completed the nitrogen cycle. So I would also suggest shopping for some micron filter pads to provide outstanding mechanical filtration the next time you stop by the fish store, such as the following, to be used if the aquarium does not clear up on its own a few days after the substrate and rockwork are added:
Micron Filter Pads
Water sparkles clean and crystal clear with Pure Flow Filter Pads. These sanitized, polyester pads are interwoven with nylon fibers, making them durable, reusable, and highly effective. They trap debris and small particles in both fresh and saltwater to prevent the clogging of biological filter media. Can be cut to fit any mechanical filter.
You’ll want to cut the micron filter pad so that it’s the right size to fit in the drip tray for your wet/dry filter. It will do a fine job of removing any fine sediments or fine particulate matter that suspended in the water column after you add the sand substrate and rockwork, if the tank doesn’t clear up on its own after a few days.. But a micron filter pad will clog up quickly, so be sure to remove it after a few days when the water has cleared up so that it doesn’t restrict the water flow to the filtration system or cause the drip tray overflow and bypass the trickle filter.
In short, you’ll want to remove the Polyfilter Pad until after the aquarium has cycled, and replace it with one of the micron-size filter pads such as the Pure Flow Filter Pads to clear up the cloudy aquarium water if need be a few days after you add the substrate and rocks.
Then you can return the Polyfilter Pad to provide chemical filtration for your aquarium after it has completed the cycling process and the biological filtration is fully established.
If necessary, you could also use a water clarifier, providing the tank does not clear up on its own after several days. Just pick up a water clarifier that is designed for use with saltwater aquariums at your LFS, such as Kent Marine Pro-Clear Saltwater Aquarium Water Clarifier. Be careful not just to grab any old water clarifier, however — many of them are designed to work in freshwater only and are not safe to use in a marine aquarium.
These products typically work by causing very fine suspended particles to flocculate or clump together so that they either settle out or are more easily filtered out, and are designed for clearing up cloudy water in an aquarium, but make sure you get one that’s designed for saltwater, not freshwater!
But that’s just to have on hand in case it’s needed. Right now the thing to do is to put your live sand and precycled rockwork in place, because those are going to make the aquarium cloudy temporarily anyway, and then see if the tank doesn’t clear up on its own over a period of days.
Best of luck preparing your new aquarium for cycling and making it crystal clear in the process!