My 26" silver aro has stopped eating since last Friday, and has been taking gulps of air from the surface way more than normal. Noticed bubbles being expelled from the vent. Any ideas? It's in a 8 × 4 × 2 with rays, and a dat. K1 filtration, drip system, temp 82, amm. 0, nitrite 0, nitrate 40-80. Anyone seen this before? He's been a big eater up till now. Had him almost 2 years with no prior issues. Raised from a baby.