I would like to know the secret to NOT spending $$$ Please tell.
I guess it's a matter of what you consider $$$$$$ LOL.
First of all my FW planted tanks have ran for up to 9 years with no mechanical filtration/circulation, no water changes, straight untreated tap water, and with descendants of the original cycle fish.
So to me what is important is to simply establish a balanced stable eco system as the very first thing.
So I start the tank with macro algae (or an algae turf scrubber which I haven't used) as the very first thing. then add fish slowly and limit feeding. the prevents the ammonia->nitrite spikes and provides a low co2 high oxygen environment. So the fish feel absolutely no stress and if fact are subjected to a healthy stable environment.
Then I do no water changes (just topoff evaporative losses) so that saves on salt costs plus the tank conditions are balanced and stable as a result.
For equipment, my sumps were inexpensive plastic storage containers. The overflow was made from $20 of pvc. So the main costs of the sump was the return motor.
The best thing I did (although not attractive to Bang LOL) was just partition the tank to form an in tank refugium. Nitrates dropped to unmeasureble in 3 weeks and phosphates followed a few months later.
To maintain calcium/alk./mag I did the improved diy two part system where $60 worth of chemicals provided literally 10+ years of dosing.
I did use, on one tank, a diy wet dry made from a wastebasket and used crushed oyster shells as the filter media.
I also had "easy" type corals and some fish were spawning as well.
I'm sure the skimmers and other system work and produce excellent tanks especially for more delicate sys type corals. So if that's your thing go for it.
I'm also sure that almost everything we have in a saltwater/reef tank can be maintained without a lot of the expense most reef tanks consume.
Edit: also no live rock no live sand as well. Got ~200 pound of limestone rock from a quarry here. $20/ton and they didn't charge for such a small amount. Sand was just common play sand 50 pound bag for $3 or so. LOL
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my .02