, I feel your pain.
If you haven't done it already, you might be able to avoid the 1:2 punch by adjusting your CO2. Even if you HAVE done the 1-2 punch I would still check this.
I set up an ADA60P at the same time as your re-scape and I'm battling with algae issues as well. Mine are almost certainly due to too much lighting and inconsistent / not enough CO2. (I switched from an in-tank to diffuser to an in-line diffuser and didn't properly tune the CO2 in). I'm on the upswing of it now and, **fingers crossed**, if things continue in their current vein, my tank should look pretty decent in a couple of weeks. To cheer you up, here is a photo of my terribly algae infested tank taken last night. Believe it or not, this is a big improvement from last week.
Your lighting period of 6 hours is reasonable and should be around 80 - 90 PAR at the substrate with your dimmer. You could maybe reduce the photoperiod to five hours but that change isn't likely to make a huge difference.
I really don't think that phosphates in your water supply have anything to do with your issues. Fresh ADA Aquasoil actually absorbs phosphates from the water column, and the amounts in tap water shouldn't be enough to imbalance your fertilization to cause an algae bloom anyway.
I strongly recommend reading this article by Dennis Wong on CO2 gas exchange. Dennis knows what he is talking about, his tanks prove it. https://www.advancedplantedtank.com/...-of-co2-safely
Drop checkers are great, but their reading is a couple of hours behind the actual level and it is difficult to know how dark green or bright green or lime green or yellow green the thing should be. Measuring your pH is a great tool in combination with your drop checker to make sure that you are really hitting 30 ppm or higher. 'Tuning' your CO2 by looking at pH is based on the concept that without CO2 injection the amount of CO2 in the water should be around 2 - 3 ppm. When you add CO2 to the tank it turns to carbonic acid and the pH drops. Given the pH-KH relationship, to get to a 30 ppm CO2 target you should see a 1 point pH drop at KH (1 - 10). (Dennis explains this way better, and also explains how you can have too slow a build up of CO2 and still be gassing your fish at the end of the day).
So do the following to check your CO2:
1) Measure your pH when it is still dark, just before your CO2 turns on. This is your baseline, your target is a 1.0 decrease in pH.
2) Keep measuring your pH every half hour or so after lights turn on. Ideally, your CO2 injection rate should get you to that 1 point pH decrease within about 3 hours or so. You definitely should be at that pH by the time your lights kick on.
3) Adjust your CO2 accordingly. Monitor your drop checker and your fish behaviour so that you have a second and third data set and aren't relying on pH alone. You may need to make adjustment to your water flow to optimize results.
Here is a chart I made to keep track of my adjustments. (My BPS are all over the place because I was playing with working pressure too and made a circulation adjustment by turning off an airstone, but you can see how it got to a nice equilibrium).
- Summer means longer daylight hours, and you can get a lot ambient light in your tank even with the lights out. Your CO2 should turn on before the tank is gets ambient daylight. For me this means my CO2 turns on at 5:30 am, even though my lights don't start up until 1 pm.
- Check to make sure that your CO2 equipment is working properly. Count and record your BPS to make sure that it is consistent throughout the day and from day-to-day. If it is not, check for leaks using soapy water and a little brush. When I switched to an in-line diffuser I didn't increase my working pressure and my BPS were all over the place.
- I remineralize my RO water to DKH of 1.8, but my KH readings are zero, or close to it, thanks to the Aquasoil, but the 1 pH drop relationship still seems to work just fine anyway.
- Where the pipes were located made a big difference for me in terms of gas exchange. I switched my pipes from the back to the side of the tank and had to almost double the BPS to hit my CO2 target. My filter has a lower flow rate than yours (I only have the Oase Filtosmart Thermo 100), but I expect you will find a big difference too depending on how you set up your flow.
Hang in there. It'll get better!