Let me break it down into two categories, lighting and nutrients.
You have 4 wpg. That means that you need a very good source of CO2. Pressurized would be best in your case. You really need to stay on top of your Red Sea kit and get it started again when it slows.
Are you using saltwater bulbs (actinic blue and ~ 10,000K) or are you using freshwater bulbs from 5000K to 10,000K? You need to be using freshwater bulbs.
If you only have one white bulb and one blue bulb, you can cut off the blue bulb if you want to.
Do you have a separate power cord for each bulb if they are OK for plant use? Put them on separate timers if you can. Run one bulb for 10 to 12 yours and the other bulb in the middle of the lighting cycle for two hours.
If you don't have separate power cords, do you have a separate on/off switch from each bulb if they are OK for plant use? If so, you may want to only run one bulb until you get you dosing in good shape.
I've been dosing with Seachem flourish potassium, nitrogen, and phosphorous since i started the tank.
I can not tell if you are using Flourish Comprehensive or not. You don't have a comma between flourish and potassium.
If you are not using Flourish (comprehensive) or another micro nutrient product as a source of micro nutrients, you need to get some.
I see that you are using the Seachem dosing amounts found when using the Seachem calculator. You should try 2x, 3x or even 4x what you get from the Seachem calculator. To get 2x, just enter 24 gallons. For the others enter 36 gallons or 48 gallons respectfully. Start at 2x and try if for 3 weeks to see how your aquarium is doing. If it is OK, then stick with the 2x dosing. If not, go to 3x for 3 weeks and so forth.
Get some Flourish Excel and only dose it at the amount for 12 gallons. You may be able to go to 2x, but don't do it if you have sensitive critters, vals and anacharis.
I'm not going into your PPS-Pro questions because you already have most of the Seachem products. You just need to get one or two more.
I hope that this helps you.