Looking at the diagram the spraybar is on the left and the internals underneath?
If so I would put 1 internal in the front right corner to move the water in a more circular motion. See if that gets some movement. Its a big tank so a long way for the filters to push along from that side
I think Radar is right in it being flow related but with non CO2 I don't think you need any more 'energy' in the tank r.e. distribution levels. I think you can just improve the way you currently have it. The Eheim intake should be next to the spraybar on the left. You are currently pushing water from the filter to the right, then it hits the glass and goes downward and then it goes back to the filter. You should always have inlet and outlet at the same end so the water that exits the filter near the water surface has to go away and then return to the same end. (circular motion, Circulation
)
You have T5HO tubes I assume and whilst only just over 1WPG t5HO are quite intense. They penetrate very well and therefore you may have patches of the tank that get intense light directly under the tube whereas at an angle not so intense. I don't mean dark patches and light patches. We are talking actual light rather than brightness so it may appear pretty even light to our eyes.
The pictures you show of staghorn in the pictures above are normally the first algae to appear when the light is high and CO2 unstable. By light being high they nearly always appear close to the tube and the higher up the tank the worse it gets. By CO2 being unstable I mean that it is a young tank, the substrate is not yet creating CO2, water changes are bringing in CO2 from the tap water etc.
There's not much you can do r.e. the lighting unless you want to totally retrofit it with less intense tubes. It shouldn't need it though. Even with them being T5HO it is within the realms of non CO2 injection territory. They do look bright in those pics of the tank though
What I would suggest is to alleviate the problems would be:
Decrease the photoperiod to 5 or 6 hours total
Stop fertilising until the new plants arrive, you're adding nutrient to already existing nutrient (from the fish waste etc) and there aren't enough plants to counter the algae threat. You basically have good conditions for algae to succeed. A full heavily planted setup will have a better chance. You may need to dose some ferts after they arrive dependent on the plants. They will tell you.
When the plants arrive I would personally (and it is a pain but should be worth it.) remove all the hardscape and give it all a good scrub. Remove fish. Get something like a pencil (or a finger
) and gently stir the whole of the sand part of the substrate (if there is a planted substrate below then you don't want to be moving that around too much.) Then remove 2 thirds of water which will take out 2 thirds of the nasties (including algae spores) that are in the water. Throw that water away. Gently gravel vac the substrate.
Reset Hardscape, add in the new plants, refill and get up to temperature. Then re-acclimitise the fish. This process could take a whole day. The fish will be fine in a container with a blanket around them for over a day.
Once you are running again, leave the lights at 5-6 hours total and then every week up it 1 hour until you are back up to 8-9 hours total.
On the fertilising front it will depend on your setup, i.e. how well the substrate works, water change regime etc. The substrate will eventually help create CO2 for the plants. The water change regime should be minimal or non existent. 10% weekly maximum unless it is vital (r.e. fish health). Try to put the plants in and then leave them where they are. Resist the urge to move them or disturb the substrate from this point on. Don't gravel vac and if you do have to move plants then do it carefully and follow it with a large (50%) or 2 medium (30%) water changes. That will remove the spike that will surge out of the substrate with disturbance.
Not sure on your fish stocks but you could add some fish that will gently and naturally disturb the substrate. YES I did say don't disturb it but I meant from not being disturbed by a plant 'reshape' and an ammonia spike (even if it is too low for a kit to register) The Bolivians will already be digging a little and sifting. Something like Corys or small plecs (pitbulls are awesome for this) or Kuhlis. They will naturally move the sand and there will be no spike. In fact there will just be a constant gentle release of free nutrient. This will also stop any build of baddies in any area that 'collects' detritus'.
So a month after the plants are in you should be back to 8-9 hours, hopefully algae free. It will take that long to see really but this is the key stage. Get that first month right and it can get pretty simple from thereon. Get it wrong and it is a ***** of a fight
If you get it right we can think about going the whole non CO2 route and eliminating water changes and minimal ferts.
If you update the journal (or link to any newer one you have) we can see how you are progressing.
If you can find something like Riccia then you could use that as a floating 'sunshade'. Grows quickly though and is hard to remove if/when you decide you don't want to remove it but that will help block some light.
AC