Grants, looking good. A few pointers if I may?
First your gonna wanna point them power heads to the surface. This will give you more water sueface agitation that will help gas exchange. It will increase evaporation but it's a good thing. Also corals dont like direct flow on to them. You have 2 very small powerheads. Not sure how you have them powered. But I would add one closet to the back and the other to the front. Give it a circler motion when they alternate.
To do this there are few ways. One use a controller such as the Neptune apex or reef keeper. These are a God send to refers. Control and moniter your tank, turn lights on, pumps on/off heater on when it's cold. Fans on when it's hot etc etc but they are pricey. Reef keeper is alot cheaper, but even a used one may set you $100. Another option is get a wave maker hydro and sicce both make one. The sicce is way better but more expensive. But for the price. You might as well save up more and get a controller.
Eventually your gonna a wanna upgrade these pumps. These will break sooner rather then later. I would recommend DC powerheads. Jeabo do some really cheap affordable ones for like $40 each. Not sure if they synch together but if they do then might worthwhile to get them now for alternative flow and use the ones you have now for dead spots and such.
Also, it looks like you need alot more rock. Unless you planned to understock there doesn't seem to be enough rock handle the bio load. If the minimal look is what you're going for the consider placing rock in your sump. Marine pure do some very porous ceramic cubes that are great for this and the up very little space, be warned that if you add lots of rock now you may start a mini cycle in your tank.
Dump that hydrometer. The thing is useless. Inaccurate and a waste. Get a refractometer, their like $20 from amazon, salinity is something you want to keep right. Don't risk it. It's not worth it.
Your powerheads are ac, so your not gonna have much control over them. If they are currently on a timer, I would say. One on from 6pm till 11am then have both on from 11am till about 6pm. Not sure what timers you are using, but I know the analog one (big dial with groves that you can push down) those are good for power heads. Since you can select the times, albeit on an hourly basis. But better then nothing. Maybe have left on for 1hr, right on for 1hr then both on for an hour and repeat. Seriously if you can afford it. Skip theivestock for now and get some jeabo DC pumps. Way better control.
Diatoms are natures way of saying you have nitrates. But don't worry they will go away. Clean up crew will sort them out NP.
Lighting period. I have mine on a 12 hour cycle. On at 9:30am. Just the leds at 15%, the ramp up to 95% at 12pm. That's when the T5s come on. From 12-4:30pm both the T5s are leds are on. T5s off at 4:30 with just the leds on. They start to ramp down to 15% around 8:30pm the off for the night at 9:30pm. My powerheads kinda follow this cycle except for the 11am where all four are at 100% to give the tank a clean from detritus. For you, I would see what are your personal preferences, what times do you view the tank most. No point having a cycle where the light are off at 6pm, when 6pm is time you have to view the danm thing. So work out a system. You have a 4bulb light right? So do a 10 or a 8 hour cycle. Let's say you view the tank at 6-7pm. With lights out 9pm. Then I would have the two lights come one at 11am, all 4 on from 1-5pm, the 2 on from 5-9pm. This will help the tank warm up from the Jo lights. Having 4 on from the start will be too much too fast for corals.
Again sorry for the long post and I hope this helps.