Well congrats on getting a scrubber into a difficult spot in your hood. You can indeed get your tank to where you want with some fixes. Here is a review of your situation:
I was recently plagued with BLACK algae looking stuff all over the sand. Really ugly and some really bright green algae on the front acrylic.
Both of these are indicators of very high nutrients in the water, and sand.
I have been flushing the tank with fresh water for about 4 weeks now and the Nitrate/Nitrites are at Zero. This didn't help one bit with that black crap.
Because the nitrate and phosphate (which may even be in the refill water) are going straight to the algae.
Here's my acrylic tray AS. 21.5x8" = 172 sq in.
It's actually half that, because yours is one-sided (scrubber sizes are based on having light on both sides.) So yours is effectively a 86 square inch screen.
Water flow is unknown and stays about 3/4 of an inch over the screens.
This does cause some slowing of the flow down at the level of the screen. You can see in your pics that growth is the most when it's nearer to the pipe. This means that the rest of your screen is not effectively filtering.
sits under a Current 65 watt CF 6500k
This is a good amount of power for one side of a screen. Also good is that it's consistant (even) from the left side of the screen to the right. It's rather narrow, however, so if it's near the top of the screen, then the bottom does not get enough light power.
It seems like the tank load is too small to support all those plants AND algae.
As you can see, plants and algae can thrive on very small amounts of nutrients. Plus, you have a lot of stored nutrients in the sand, built up over time.
If I wait longer than the 7 days it will get very thick and come off in sheets.
Can't have that.
You need to scrape off the algae every week in a salt tank.
Fresh too.
It's about to grow down the 'down spout'
Can't have that either.
OK, now your situation is clear. Your black algae is still a problem because:
1) Your scrubber is just too small in size for your tank.
2) Your scrubber is only partially being used.
3) You have an in-tank scrubber already (on the sand, and on the glass).
1) From the basic size recommendations, your 130 gal tank needs a 130 square inch screen, lit on both sides. For a single-sided version, you have to double this, and double the lighting on the one side. So you need 260 square inches of one-sided screen. You currently have 172.
And from the basic lighting recommendations, your 130 gal tank needs 130 watts for high filtering, or 65 watts for medium filtering. You have 65 watts.
2) Your flow is coming out of just one spot. So, the flow will be strong in that immediate area, but weak further way, and zero in the corners. Plus you have a thick level of standing water (3/4", because the screen is not tilted), so flow is even less at the level of the screen than it is at the surface of the water. So beyond about 5" from the pipe, you have no filtering.
About the lighting: the distance is perfect near the bulb, but at the opposite end of the screen, it is too far away. So beyond about 4" from the bulb, you have no filtering.
3) Whenever you start a scrubber on a tank which already has lots of nuisance algae, you have to overpower that algae with the strengh of your scrubber. This means stronger light, stronger flow, rougher screen, and larger size, than is normally recommended for a given tank size. After the nuisance algae has reduced, you can then reduce your scrubber to a normal size. The other way of doing this is to weaken the algae in the tank with reduced lighting, until your scrubber can overpower it.
So, although your growth "looks" great, it's actually just not enough to do what you want. On paper you have a 65 square inch scrubber on a 130 gal tank with a high nutrient problem; but since your screen is not fully covered in flow and light, I'd say you have half that... about a 30 square inch scrubber, on a 130 gal tank with high nutrients. And that is the problem. You can definately solve this with enough scrubber power; it's just a matter of how far you need to go. So here are some fixes for you to consider:
1. Most important: Make the flow strong and consistent from one end to the other, by moving the pipe to one end, and having two (not one) drains at the other. If you can also tilt the screen, this will speed up the flow. And if you can add another pipe of incoming water, this will help even more. What you want is a river-rapids appearance that is very thin. This fix alone will at least make full use of the square inches that you have.
2. Add another lighting unit. This will make use of the screen that is further than 4" from the bulb, and will put you at 130 watts for 130 gal, which is what you want for high filtering (and is what you need when you have high nutrients, or when you have pre-existing large amounts of algae in the tank.)
3. Clean your screens before algae starts going down the spout(s). By the time you can see algae at the spout, a hundred times more has already let go and gone into the tank. If you like feeding your fish this way, then don't feed them anything else.
4. Last resort, only to be done after all three items above: Add another scrubber to the other side of the hood. And if you do this, incorporate all the fixes from the beginning.
I think that by just fixing the flow and the lights, and by cleaning more often, your one scrubber will have all the algae off of your sand withing 8 weeks. Your need to clean the glass will be reduced greatly too in just a few weeks.
