Not for nothing, but the trend for at least the last 5-8 years has been to use what is referred to as “live sand” and “live rock.” Both are harvested from various oceans around the world and help a reef aquarium keep most of its flora AND fauna. It is exactly those things that help define the prices of said items.
There is actually a local farmer here that “makes” live rock. If you want to learn more about it, checkTampa Bay Saltwater You can see how the whole operation works. Once upon a time, they had a retail store you could go into. However, they are entirely phone/web now.
Aquariums have long gone past the plastic plants and fake rocks. It is rather amazing at the technology that can go into a tank.
This site Oregon Reef is of persons tank. It is an amazing reef tank and very, very well done. He changes out his live sand every couple of weeks because he thinks it looks better that way. That is a pretty heavy investment for that kind of return. To give you an idea, a “package” deal from Tampa Bay Saltwater, that has all the rock, sand, “cleaning crew” for a 55 g. aquarium is $690. They sell rock from the Gulf of Mexico. Many other types of rock, like Fiji Rock is far more expensive than TBS’s.
Now, back to the OP. Contaminants are the issue. It’s not necessarily what is living in the water, but rather what we are dumping into it. Most of the critters that habitate said rock/sand/water are pretty well known in the community. What we don’t know is WTH shady company X has poured out and that close to shore, it doesn’t have much room to swish around and get diluted. When you are talking about the kind of money that some of These are investing in their tanks and existing livestock, it is much more cost effective to be safer than sorrier.
I have a freshwater tank and I had a weather loach go over the overflow, through the wet/dry filter and clog the pump. $10 loach, $10 worth of mollies, a $3.99 cory and $20 worth of plumbing supplies, about 3 hours labor. Saltwater fish, excluding damsels, are routinely far in excess of $30 a fish.
Some say keeping saltwater tanks is like standing over a toilet and flushing money down it. That being said, it is a fascinating and rewarding hobby, moreso now than ever and the enjoyment I get from my tanks is well worth the investment.
My grandparents lived on the Gulf for many years and had tanks. The kids caught little fish and things and they changed the water frequently, heck, it was their back yard. It was a pretty low tech setup. It can be done, just probably not with a successful reef tank.