My tank is about 3 months old. My nitrates are between 5-10ppm.
It's a 75gal w/ 265w PC a 4" DSB and so far I have accumulated 45lbs
of
LR.

No. You are way under par for the amount of LR, aim for 1.5-2.0 lb per
gallon depending on LR quality.

With the proper amount of LR and 4" of DSB, your nitrate should be zero.

jc