Do a search for this topic and you will find plenty of responses. Basically though, salt mixes should take care of all of those. You may need to add extra calcium. But you will find that the less chemicals you add to your tank, the better it will thrive. I only add calcium to my tank currently and its never been nicer.
I happen to agree with HairTrigger. If you keep up on regular water changes there is no need to add all the extra chemicals. Calcium will need to be added. Do you guys test for Iodine, Strontium/Molybdenum before you dump a bunch of it in your tank?
You ask how to keep the alk up? By water changes. How does your alk get into your tank when you first set it up? From the salt mix.
I also agree with HairTrigger and Slick. Some time before i was always adding additives on weekly basis. Then i stoped with everything and left with 10% biweekly water changes only. Calcification rates and growth rates increased dramatically with most slow growing corals! Ones Ca and Alk are adjusted, the only thing is being added (topped-off) is kalkwasser. I keep Kent Marine's Turbo Calcium and buffers just in case if Ca or Alk levels will drop suddenly due to increased depletion.
P.S. It was said that Xenia requires extra iodine. I don't add it and it spreads like crazy
Anyways, i would say, that don't add whatever you cannot or don't test for. Especially iodine, as it can reach toxic levels if not being used up.
I don't think many people consider DT's a 'chemical' ? And like baraccuda said, it's not good to add supplements for things you aren't testing for.
I think it all comes down to the methodology you choose to use. Some will use chemicals on a as needed basis, only supplementing those things that are depleted (takes a lot more understanding and time). Some just do their monthly (or so) water changes and add calcium/alk buffer (which many methods of calcium addition also will raise alkalinity as far as I understand). Then there are the people who use 2 part (which seems to be a good percentage) where you don't have to necessarily test each particular element, but monitor your levels of alk, calcium and pH regularly in addition to frequent water changes and you will keep a relatively good ionic balance.
And these are only a few of the methods. There are countless combinations. It seems easiest however, to start with something basic until you understand the relationships within the system. Since some ions can combine with others in an equilibrium, if you add too much of that one it will use up all of that counterpart, depleting the element. This, as far as I've been able to research thus far, is why it is usually recommended to add both calcium and magnesium supplements when using the liquid supplements. Those forms of calcium will use up magnesium by creating a bond, making both unusable if too much calcium is added without a balance in magnesium.
Anyway, take any regiment of additions slow. Even add only half the recommended dose first. Then check your levels, see what's going on before continuing with more. If it all goes awry, do a water change or two more frequently than normal; balance should be restored.
This is probably one of the most complicated aspects of the whole reef keeping experience (other than expense) because there are so many options, and there isn't an easy way to understand it all.
I'm another of those that prefers to avoid adding trace elements that I do not test for. Any quality salt mix will normally replenish trace elements at close to natural saltwater levels...and regular 5%-10% water changes will maintain trace elements. I do add for calcium/alkalinity and I drip kalk to help maintain established levels of calcium/alkalinity...but I do not add any other elements/chemicals to my system.
Put me down for agreeing with hairtrigger. I count on waterchanges and never add what I can't test for. Do your water changes and be observant most tanks speak to you ... you just have to listen and be patient. Yes it helps to speak fishy
When adding calcium, it will boost your alkalinity (dependant on your calcium source) so that might be where he maintains his alk from.
For example, the hydroxide in the Calcium Hydroxide (kalkwasser) provides hydroxyls to provide a equilibrium to maintain ph. the hydroxyls are held by other elements in the aquarium. Which ones i'm still trying to figure out. But it does work... I've been looking for equations to provide more insight to this.
I do things a little different. I do a 25% water change every couple of months and add a capful of iodine, Strontium/Molybdenum, and coral vite every month that I don't do a water change. Seems to work for me.
Banshee, i don't think that adding chemicals as you add is bad idea. But even then it's not prooven that you need to add those additives. If i were you, i would do smaller and more frequent water changes and don't add that stuff you're used to add.
Adding "trace" elements makes the reef keeper feel good ~ but I doubt it does much for the tank.
Most good synthetic saltmixes contain FAR MORE concentrations of these chemical compounds/elements than natural seawater.
Simple water changes every 4-6 weeks is all I do regarding this area of the water chemistry.
Alkalinity, calcium and pH on the other hand - should be monitored and "controlled" by some form - which is up to each reef keeper.
There are plenty of proven ways to do this - each work fine ~ some work better than others.
Bottles of "trace" elements, and vital this and vite that and essential this and other products - I avoid completely now.
It very easy to whack out your water chemistry adding stuff you do not test for - nor have any clue what the proper dose is to begin with. Unless you just read the instructions on the bottle and believe what you read.
The wonderful things on the bottle sound good don't they ?
For $20.00 a bottle - they should sound good.
Save your money - put it towards lighting, a good skimmer or calcium reactor - something else that is 'KNOWN" to help.
Maintain cal,alk and ph with additions of calcium and buffer. Ea tank is different. But trace comes from many sources= w/c and feedings of good foods. If you feed everyday you can look at your food source. Some foods contain 100-10,000x more traces parts than NSW. As for live rock you don't need to add anything to keep it LIVE. cal and alk will help the coralinne but the SW should have enough cuz if you don't have corals nothing is getting consumed in great amounts. What makes LR live is the bacteria and "bugs" in the rock. You may want to feed alittle now and then .But every tank is different and theres many ways to keep one just don't fall into you must have. Wait you must keep cal alk and ph in check everything else is debatable