Questions - Need some input

Well after 4-5 weeks my cycle is complete

The two table shrimp are pretty much gone, ammonia is 0, nitrite is 0, and nitrates are between 0 and 5 ppm.. Temp is 77-78 degrees, salinity is right on the mark. Calcium seemed high at like 480-500 but it was my first test and not sure if i did it right.

Did a 5 gallon water change today.

But im concerned as I havent seen any algae or diatom blooms.....i have read many start up threads with these and im wondering ...

So I came home, and found my return pump sucking air and blowing it into the DT.

Open the cabinet doors to find the water level in the return area was low....
now I know the water level didnt evaporate that much as I added like 2-3 gallons of top off yesterday.I adjusted the return pump flow down to allow the water to catch back up and then was able to open the valve completely open again and things stabilized and no issues....I added another gallon of top off just to be safe... ...

Anyone ever heard of and or know how this thing works?

Got 2 protein skimmers for 20 off craigslist, the other is used and Its designed to where you cant really clean inside. The other is a Sea thru aquarium products, looks brand new, other than some scratches, but the lady knew nothing about it. I used a 350 pump with aeration attachment but the flow was so strong no bubbles formed and just blew water out the top. Then I got an air pump to add more air but having same problem. ...

Ok so I havent been doing anything with my salt water build. Life got in the way and with a possible move decided i didnt want to get a tank up to just tear it down. Now the move has been put off for a few years so I want to get it up and running.

Still have to finish sump, build/fix the overflow box, create my live rock and buy good lights.

I am looking at doing fish and some soft corals to start.

I was originally looking at an Odyssea T5 216 watt light ...

Ok so the lady brought home the "75G tank" which actually turns out is the same size as my 55 g.... so its a 55 g.... anyway not to bad condition there are some scratches on it and it appears that the bracing on the top has some small cracks but still in tack.

I filled it with water outside to test it and the top seems to hold fine but there is obvious bowing in the middle of the front and back panes.... Is this normal for acrylic? Never owned one but assume since its plastic ...