Let me start with the fact that this was not my horse, nor my goldfish. But, this is under my care now. 

Close family member chose to put 2 goldfish, despite my recommendation not to. (Utter horror, really.) 100g water trough. Built in heater type.

I am an avid indoor keeper. 13 planted tanks. So, I do know my aquarium stuff for the most part. And, apparently, this a common fix for algae, to put fish in farm animals water. I had no idea this was a thing. Yet, it is. 

Anyways.

The family members horse passed last week and the trough wasn't getting any top offs or attention whatsoever. 

I get it, kinda. Grief for the horse. Valid. But, we can't just abandon the horses "pets" now... 

Took matters into my own hands. 50% water change & added water lettuce for them yesterday. At the very least.

They seem much happier. Never had or watched goldies long enough to see this behavior before. 

Are they okay for now?

What kind of water filtration do I need to add? 

I don't have ponds yet, but I would like to learn. Universe just threw it at me early, I guess. 

I need something good enough for goldfish, but less surface agitation for water lettuce? Something that can be outdoors easily. (Sponge filters/hobs are bunk here. Got lots of extras of those.) 

I am stumped.

Any advice is welcomed. TYIA 💛

Goldfish in horse trough. Horse passed away. Need advice.