Any Suggestions

[Glassman]

Posted last night that I lost my Zebra oto. Got up this morning and my German Blue Ram was dead. I tested my water and nothing looks wrong to me. I am new to this so what do you think. My tank is a 37 gallon planted tank with 9 Rasboras, 3 Corys, 3 Otos, 2 YoYos, 2 Scarlet Badis, and now 1 Female GBR.

Nitrate 18ppm
Nitrite 0 ppm
Hardness 75 ppm
Alkalinity 85 ppm
PH 7.2
Ammonia 0ppm

I plan to do a 30% water change now. Any help or suggestions are welcome.