More drama! Loaches breathing poorly

To add to this already dramatic day (see betta rescue), we have now discovered our two Yoyo loaches in our 18 gallon are breathing VERY rapidly, and acting somewhat reclusive. Everyone else in the tank seems to be acting normally. We did add two Ottos 3 days ago, but they seem healthy and keep to themselves. The loaches were fine this weekend. Water looks good - ammonia 0, nitrites 0, ph 7.2.

Any ideas?

We just did a massive 50% water change hoping it may help.

thanks all