(you're missing filtration which is the most important)
Honestly it's much more affordable to buy an all in one like a biocube or nuvo. I think nuvo looks better than cubes do. If you're going to be doing fish+corals you're going to have to do either or a combination of these three... weekly to biweekly 15%-25% water changes, an HOB- (hang on the back) or in tank protein skimmer, a hang on the back sump for sufficient biological filtration, keeping the amount of fish to no more than two 3 inch fish. Aside from these method to preserve water quality & assuming you would not get a protein skimmer I would also add to that a hang on the back cartridge filter rated for at least double the amount of water you're using it for. Me personally? This is what I would do. Use an HOB sump with bio beads & seachem "matrix" or "de nitrate"- (both are for bio filtration & will remove nitrate much better then live rock or beads, de nitrate being more expensive). Then I would add an HOB cartridge filter unless you can fit filter floss into the HOB sump some where. Ussually, hobbiest will tell you 1lb of live rock & substrate for every g of water. Extremist usually will tell you 2lbs per g of water. I say 1lb because with the help of your thriving bio filtration, it will more than do. On my system this is pretty much the bio filtration I have along side activated carbon, zeolite crystals, & phosphate absorber- (all of which chemical filtration). There are a plethora of different chemical filters out there. What you want to concentrate on is if it can remove organics, ammonia, & nitrates. Seachem I think also produces something like this that way you don't have to buy several medias of filtration. moving on to the salt mixing process. Keep in mind that unless you're buying premade SW you are going to have to buy an R/O water filter unit so that you can mix it with the salt. If you use tap water (dechlorinated abiously), you're going to get an uncontrollable algea bloom form the nutrients in tap water. You could buy the water in bottles but that would be VERY expensive. Also, their is no salt mix pack for under 25g. The reason I bring this up is because if you're not planning on using the entire pack, you're going to have a hard time. These salts absorb water VERY VERY easily & the problem is that once they become hard, they crystalyze & wont mix properly in the water. The only solution to this is to make the entire batch in whatever container*s & keep the saltmix mixing with a pump & covered (not very practical). Of course the other best option is to just buy pre-made water which also brings up another point. Their is un filtered & unsteralized ocean water, filtered & steralized ocean water (petco or other brand online) & pre made salt mix water. Use either the premade or the petco stuff because any live rock, live water, whatever that comes from the ocean or another tank exposed to oceanic live micro organizims can pottentially carry parasites such as ick or parasitic inverts. Moving on to live rock. Live just means that it contains living organisms wether bacterial or large enough to see with the eye. Live rock depending on where it comes from (wheter it's from the ocean or was seeded bu another live rock) is a double edged sword. They can bring both good & bad life. That's why it's better to just buy regular rock (much less expensive) & over time it will become live with good anerobic bacteria that bio filters your water or if you do get live rock from anyone make sure to kill everything in it by washing with tap water, brush it off, leaving it in the sun for 2weeks, & the finally cure it in a bucket until it stops realesing amonia. Moving on, hydrometers are fine but, they're very delicate. You must make sure that you ALWAY ALWAYS wash & clean it with tap water after using it with SW & never drop it. It may work after dropping but it also may not. Light, any light is good for any SW fish. The only purpose in fact is just for the fish to know that it's day time & behave accordingly since these fish DO actually rest. For corals you'll have to buy a light fixture that supports at least two bulbs. There are many, here's the cheapest company
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Strips suck, & usually are inacurate, just get a digital one. For water flow you'll need a circulation pump. You'll also need to supplement the tank with chemicals (nano two part dosing) to keep the minerals high enough for the corals depending on how many corals you have- (how much minerals they are absorbing form the water) & how many water changes you do. Remember to always quarantine & medicate fish in a separate tank as well as dipping corals & quarantining them in a separate tank or container for at least two days, same goes with macroalgea. It's not a 100% guarantee but, if you don't you'll risk infecting your fish & or corals with parasites. Make sure to also cycle the tank with bio-spira according to the amount of fish you have once the fish are in & the whole system is a go. GOOD LUCK!