Water Quality

 This is the part where things get messy and complex. Yes, we are talking about water chemistry. I will explain to the best of my abilities what to look out for and some experiences here and there.

Mixing Saltwater
I think this is pretty simple. Choose a salt that has the parameters you want to maintain and mix it into clean freshwater. By clean freshwater I mean 0 TDS water, for me I would allow a TDS of up to 5 and that's it, would change my RO/DI cannisters the moment I see a 5. TDS stands for total dissolved solids, it is the measurement for the total concentration of dissolved substances in the water. The concept is that you want to strip everything your water has and depend on your salt to give you whatever you need for your tank to thrive. The reason why is because you do not know what's in the water, let's say it has a 50 TDS reading, the dissolved substances in it may be toxic, it may not, it may be excessive iron due to rusty plumbing and the list goes on. You could spend a good $60 to get an ICP test to know what's exactly in it but I wouldn't spend that money to do so. Distilled water in supermarkets work too but the best way would be to get your own RO/DI system and make your own water, helps to save up in the long run. Salt wise, I use Tropic Marin's Bio-Actif at the moment as it is close to the parameters I want to achieve and it does a quick clean mix. When mixing the freshwater and salt, always water first before salt. If you do it the other way round, precipitation will form.

https://www.carousell.sg/p/new-4-stages-di-water-filtration-with-tds-pen-and-di-resin-zero-tds-with-zero-wasted-water-selling-since-2015-good-set-good-feedback-not-in-for-quick-10-feb-2021-stock-ideal-for-shrimp-marine-fish-rodi-ro-di-137414188/?t-id=357047_1614687104065&t-referrer_browse_type=search_results&t-referrer_request_id=TZuJtYJKVZPMk8ep&t-referrer_search_query=4%20stage%20ro%20di%20system&t-referrer_sort_by=popular

Salinity
This is the easy part, a refractometer pointing to a good 35ppt or 1.026 SG will be good. It is important to keep this stable. How? Top up water once it evaporates, one trick I learnt is that I put a small tape on my sump tank which will mark my current water level when I get the salinity right, every alternate day I will check in on that and top up with freshwater (RO/DI water). Small fluctuations are acceptable for most corals but I wouldn't risk it. Recently, I got lazy and installed a auto water top off.

The Big Three
I won't dive into the individual components, but the big three comprise of your calcium, alkalinity and magnesium. I like to keep my calcium at 420-440ppm, alkalinity 8-8.5 and magnesium 1350-1400ppm. These are the core for your coral growth. It is crucial to stabilize these parameters especially alkalinity. Calcium and alkalinity will be consumed the most, hence most people use 2 part dosing or calcium reactors to 'top up' the consumed portions instead of doing water changes. Also to note, I found the best alkalinity to be kept is within the 8-10 range, never let it fluctuate that much, I keep mine at a +-0.2 maximum, corals hate it when alkalinity fluctuates too much within a day. Why 8-10? Alkalinity goes hand in hand with water PH, corals maximize growth when the PH is kept at the 8.2-8.3 range and stable, higher alkalinity helps to keep PH stable, let's just say it doesn't swing that much and you won't have as much trouble keeping it stable compared to alkalinity 7 tanks. Magnesium is something that you won't have to be that concerned about, although it is one of the big three, most corals even SPS are forgiving when it comes to magnesium. The reason is because magnesium is consumed less compared to calcium and alkalinity, I would say at a rate almost 1/3 slower. I used to test calcium and alkalinity every 2 weeks while magnesium would be a month.

Nutrients
Basically fish poop or decomposed food will produce nitrates and phosphates. So these are what your corals feed on to stay alive. Make no mistake, this is different from the big three. Nutrients keep your coral fed while the big three gives them the ability to grow. Too little nutrients = starving corals, too much nutrients = algae bloom. In my experience, keeping nitrates at 5-10ppm and phosphates at 0.03-0.1ppm is the optimum, ideally phosphate as close to 0.03ppm as you possibly can, it makes a noticeable difference when it comes to coral coloration.

Trace Elements
Hmmm these are the stuff I honestly feel you don't have to test for it unless your corals all start losing a specific color or your salt does not include it. Usually weekly water changes should replenish the lost trace elements consumed by your corals so I wouldn't worry about these.

Heavy Metals
Toxic stuff. Avoid things like rusty screws in equipment, rusty light handles, etc. Anything with rust basically spells a big NO. Always wash your hands with soap and clean them well before dipping your hands into the tank. I like to run ReefSpec carbon to help me keep these in check, kind of like a safeguard measure but hey, better be safe than sorry.

Ammonia & Nitrite
Ammonia is a big issue. Anything more than 0.15ppm you should not add livestock into your tank because its considered a hazard. Fishes will die from ammonia burns and poisoning. I don't test for nitrites because I don't believe in testing for it. If I find low ammonia + higher nitrate reading, it means the tank is good to go. But if it's low ammonia + low nitrate readings, it points out your cycle or bacteria colony has issues and there will be lots of nitrites present.

Clarity
I use ReefSpec carbon and UWC's Vibrant as a means to keep it nice and clear, but running AquaUV kicks it up a notch, my water literally looks like air, it's like its not even there, of course the random micro air bubble reminds me that it's still a tank with saltwater.