You don't need an OTDR. Nice to have, but not needed.
Get yourself a optical fiber meter that works at least with 1310 nm.
Disconnect the fiber from the TX and measure the launch strength at the device's TX output in db. Then reconnect fiber at the TX end only and go to the far end of the fiber and measure the strength before it hits the RX. That db reading should be within 11db of launch to be in your budget. Hopefully within 7-8 db.
Sometimes you put a barrel at the far end and just loop the signal back to check the full run of fiber.
It would be better to know the minimum launch strength of the TX in case you have a bad laser/LED. But if measure enough devices, you will have an idea of the launch strength.
Clean all connections, get an FIS fiber cleaning kit for ST. Clean every time before you patch. Minimize any fiber joints, you can see up to 2db loss in each joint, more if they are dirty.
Don't ever zip tie fibers, pinching them is really bad.
Watch for minimum bend radius, sharp corners. Can you visually inspect the fiber run? Who ran the fiber?
What exact fiber are you using? Who terminated the ends? Are you using any fiber barrels? What is the spec on the fiber ends(PC, UPC)?
Are you having issues on short runs? I've seen gear not happy with too much signal, so you have to use an attenuator. Rare, but a possibility.
As a rule with fiber, ALWAYS run extra strands. I usually run a TAC-4 when I need only 2 strands. Future proofing and redundancy.
I've worked with 500-1000 ft runs up to a few miles. Mostly with ST singlemode. Never trust old fiber unless you know who ran it, how they ran it. You need the right
tools for measuring, cleaning, polishing and terminating. You also need to know how to use the tools. I don't polish or terminate, just know when to call in the fiber techs.
I use fiber only when copper won't reach. The extra hassle, cost of fiber, and having one more thing to fail is not worth it for short runs.