Yep. All I read was blah, blah, blah. That cemented it for me. No DIY!!!Depending on your comfort level.. I would DIY it. I just did mine.
If you have 2x8 joists I would sister in another 2x8 to each existing. I would look if there are any seams in the plywood near where you are putting the tank. If so, I would block it as well. Blocking provides a lot of strength and keeps the joists from sagging.
I would dig a footing about 12 inches deep and wide enough to put a pier block in. Pour some concrete with a little steel to give it strength. Then put the pier bloc on. You could replace the pier block with a screw jack if you want but the concrete you pour must be troweled flat. Place a 4x4 that spans all the joists where the tank will sit. This should be done at 24 inch intervals.
I would check to see if your floor decking is 3/4 inch.. most likely is. I would most likely block it every 12-16 inches if it was 3/4 inch.
That should provide enough support. Is your crawl space dirt?