Dosing magnesium? Calcium?

Had to dose 15ml of each today. (mag, cal and alk) I'm basically dosing my guess at my tank volume 20 gallon tank minus rocks sand all that jazz. I'm guessing maybe around 15 gallons. I'm thinking 15 ml is going to be my daily number. Just a guess though. Still want to check it for a week or so. See if that's consistent. What's a normal alk drop within 24 hrs? Any ideas? Also since I'm dosing manually, thing is due to my work schedule I dose go to work, by the time I get home lights have been out for like 4 hrs. I know testing for pH when the lights have been out will effect the outcome. What about the 3 I'm testing for? Is it ok to test for them after lights out our will it mess up the accuracy?
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I wish I could tell you a "normal" number for dosing, it all depends on your amount of corals and their growth. I do find it kind of odd that all are being depleted the same amount. Alk should be the most followed by cal and then mag. I'm dosing 1/3 the amount of cal that I am of alk for your reference, but once again it all depends on your system.
Well that won't bring me back to my exact numbers but damn near close with 10 ppm for cal and mag. Alk will be 8.3 instead of 8. Is this OK? Or should I be aiming for the exact numbers I'm looking for. I kind of made it all 15 ml just cause it was easy without varying my numbers to far off.
8.3 is fine, stay lower than 8.4. Are you checking your parameters before dosing? You can make your own mixture for alk with baking soda and not raise your ph. You need to cook it in the oven at 300 degrees for an hour. Google making alk with baking soda for a reef tank. I don't know how to link it to here. Most alk pre made mix will buffer to 8.3, so I'd say your right on for now.
Ya I always check before dosing. I just don't want to keep having too. Lol. I figure if it's a consistent drop everyday for a week. I should be able to dose without checking every day. Alk does seem to be the one that drops the most. I'm aiming to keep my calcium around 450 alk 8 and mag 1400. I will check that out about the baking soda. I have been monitoring my pH as well doesn't fluctuate very much 8.0-8.2
All those recipes are stronger than the store bought pre made solutions, so your going to have to find out where you need to be again. You will save alot of money and you can make all 3 major elements at home. If I remember correctly, the gallon of pre made alk is 6800dkh. Keep it in mind.
Honestly it's fine. 7 to 12 is where the magic happens, more experienced reefers keep it at the 7 to 8 range. They say they have better results in this range. Now from me and not hear say, I aim for dead nuts 8.
so I tested today, 3 days after my water change and these were the numbers

after WC: CAL 450, ALK 9.6, MAG 1400

Today CAL 450, ALK 8.7, Mag 1340

does it make sense that mag would drop that fast along with alk but my calcium is the same?
Ok, time to be Debbie downer, you will be chasing your numbers there too. Your tank is far to new for there to be issues that a simple w/c can do for you. Your selection of corals that you have with size in mind should not require this expense. If your tank was on the full side of it I would understand. I just don't like seeing folks waste money on things that won't make a lick of difference. If it makes you happy to have all the gadgets, then I guess do it. The question I guess I have is, did you ever try to lengthen your w/c schedule like previously stated? This small practical decision may be all your system needs. Please don't chase numbers, that is all they are.
I have considered that but I was really looking for consistency you know...the last WC I did was last week, I added the solution to the numbers I wanted and by the time a week was up my calcium was below 400 and alk had dropped to almost 7's

I guess I could do just WC's but really wanted a less maintenance tank

Also, I have had tanks up for 5-7 months and never had coraline grow yet I see these 3 month old tanks with crazy coraline and thriving coral

the only thing I have been able to semi grow is zoanthids
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At about the year mark for my tank is where I started dosing (fairly recently). I couldn't achieve above 6dkh. This is when I was torn between cal. Reactor or dosing. The cal reactors are so unreliable, I've seen reefers with 4 5g buckets full of dead coral because of a hiccup in their system. These are very heavily stocked tanks and I am on the verge of this. I have no spot to place corals and this is when I decided that I needed more to maintain. With my dosing pumps, depends where I test and what time I test will give me all different numbers. You should have the same everywhere, but this is not true, water naturally fluctuates threw the day and your tests need to be routine. I would say that your numbers aren't all over the board and they will not affect growth of your corals. At this point enjoy and set back. Stop testing all the time! :-)