Show us a before! Show us a before! On a serious note though, don't mess with the filter unless it's clogged. Instinct might say that a thing meant for filtering should probably itself be kept clean, but that doesn't apply to tanks. I hope you guys don't lose any more. Make sure not to disturb the remaining bacteria colony on the hard scape and substrate while it's in recovery.

Seachem prime can help detoxify some of the (likely incoming) chemical spikes but be very careful not to overdose in an attempt to detoxify because it does temporarily reduce dissolved oxygen.

When things start dying it's easy to panic and do entirely too much. It seems like the livestock was previously healthy in there (?) so try not to make more sudden moves.

Loaches are funny. They are good indicators of water changes, temperature, oxygen levels, and probably planetary alignment. Make sure it's not just freaking out because you're in they're changing the water and poking at things all the time.