This is oddly enough one of the things new hobbyists often think least about. They obsess over equipment and fish and rock and sand...
But...whoa, there. WATER is everything that determines life and health of your fish and corals.
First of all: YES, first fill should be ro/di with zero TDS. (total dissolved solids)
YES, you need to cycle fully.
Second: if you're only fish, you can use salt that's not for reef.
If you want corals, start with reef salt.
Third: plan to have a cuc at work after cycle for a few weeks while you make your beginner mistakes and while your SINGLE fish or pair is in quarantine. Because there ARE beginner mistakes. And that cuc is preparing that sandbed for something more demanding.
Fourth: set your temperature about 79 and hold it. Set your salinity. For inverts and corals your salinity needs to be 1.024 to 1.026 and STEADY. You need an ATO, and you need to know how not to flood your floor or change the salinity. You need to know that things will survive the rapid drop of salinity, but if you are RAISING salinity, you should go no faster than .02 jump per 5 minutes even with HARDY specimens.
Fifth: Pre-set your qt to the salinity of your store. Ask them. ---Then don't acclimate at all---just put your new specimen into the qt and take your sweet time bringing the salinity up over days, not minutes.
Sixth: NEVER let store water touch your qt, and certainly never your tank. It could contain copper, which is not good for your sandbed or inverts. It could carry parasites or disease. Keep it out.
Seventh: EVERY tank should be testing alkalinity as soon as the cycle is done and the CUC goes in. It should ride between 7.9 and 8.3---can be higher, but should not be lower than 7.9. Use DKH buffer to keep it up, among other means. You need an alkalinity test. (Mine is Salifert, which is numerical in output. You WANT numbers, not colors on this one. It's too critical.) If your alkalinity is off, nothing's happy, not fish, not inverts, not corals. It's as basic as salt. And never mind tracking ph unless something's clearly squirrel. Ph bounces up and down during a single day. Alkalinity in a marine tank tells the real situation.
Eighth: If you keep stony coral you need two more tests, at least: and do not neglect testing nitrate. You want it as far down as you can get it. The two tests are calcium and magnesium. Here's a secret. If you have your alk at 8.3, your cal at 420 and your mg at 1350 (at least above 1200) those three readings will not budge if you put kalk (lime) into your topoff ro/di water. As long as the mg stays up, the kalk will hold the other two up. When the slow use of mg by the corals finally depletes the mg, the alk and cal will start to sag like a deflated tent. Restore the readings by dosing, restart the kalk, and it holds like magic. This is how you can go on a month's vacation in the assurance your stony reef is well-fed and happy while you're gone.
Ninth: if your tank for some reason starts downhill toward a crash, priority is getting all the healthy specimens including loose corals and inverts out to good water that need not be made from ro/di (Prime or Amquel will 'condition' it) and need not be cycled, just aerated and heated. Relieve the load on that struggling tank and start water changes and you may avert the crash, while all your healthy specimens are safe in clean water.
But...whoa, there. WATER is everything that determines life and health of your fish and corals.
First of all: YES, first fill should be ro/di with zero TDS. (total dissolved solids)
YES, you need to cycle fully.
Second: if you're only fish, you can use salt that's not for reef.
If you want corals, start with reef salt.
Third: plan to have a cuc at work after cycle for a few weeks while you make your beginner mistakes and while your SINGLE fish or pair is in quarantine. Because there ARE beginner mistakes. And that cuc is preparing that sandbed for something more demanding.
Fourth: set your temperature about 79 and hold it. Set your salinity. For inverts and corals your salinity needs to be 1.024 to 1.026 and STEADY. You need an ATO, and you need to know how not to flood your floor or change the salinity. You need to know that things will survive the rapid drop of salinity, but if you are RAISING salinity, you should go no faster than .02 jump per 5 minutes even with HARDY specimens.
Fifth: Pre-set your qt to the salinity of your store. Ask them. ---Then don't acclimate at all---just put your new specimen into the qt and take your sweet time bringing the salinity up over days, not minutes.
Sixth: NEVER let store water touch your qt, and certainly never your tank. It could contain copper, which is not good for your sandbed or inverts. It could carry parasites or disease. Keep it out.
Seventh: EVERY tank should be testing alkalinity as soon as the cycle is done and the CUC goes in. It should ride between 7.9 and 8.3---can be higher, but should not be lower than 7.9. Use DKH buffer to keep it up, among other means. You need an alkalinity test. (Mine is Salifert, which is numerical in output. You WANT numbers, not colors on this one. It's too critical.) If your alkalinity is off, nothing's happy, not fish, not inverts, not corals. It's as basic as salt. And never mind tracking ph unless something's clearly squirrel. Ph bounces up and down during a single day. Alkalinity in a marine tank tells the real situation.
Eighth: If you keep stony coral you need two more tests, at least: and do not neglect testing nitrate. You want it as far down as you can get it. The two tests are calcium and magnesium. Here's a secret. If you have your alk at 8.3, your cal at 420 and your mg at 1350 (at least above 1200) those three readings will not budge if you put kalk (lime) into your topoff ro/di water. As long as the mg stays up, the kalk will hold the other two up. When the slow use of mg by the corals finally depletes the mg, the alk and cal will start to sag like a deflated tent. Restore the readings by dosing, restart the kalk, and it holds like magic. This is how you can go on a month's vacation in the assurance your stony reef is well-fed and happy while you're gone.
Ninth: if your tank for some reason starts downhill toward a crash, priority is getting all the healthy specimens including loose corals and inverts out to good water that need not be made from ro/di (Prime or Amquel will 'condition' it) and need not be cycled, just aerated and heated. Relieve the load on that struggling tank and start water changes and you may avert the crash, while all your healthy specimens are safe in clean water.
Mistakes? I've made a few spectacular ones along the way...but systems change and there's always something to learn. This forum is where the newest in hardware meets the newest in hobbyists, and I learn in here, too.
