Is Alk stability Key to SPS Health

[Randy Holmes-Farley Verified Community Expert]

I find that alk stability is important, but that Mg is the key to that stability. If I see a swing of +/- 100ppm or greater of Mg, the coral begin to deteriorate due to the subsequent swing in alk. This is what I have observed over the last couple years of coral keeping. I maintain Mg at ~1400ppm as this is what works for my tank. This keeps alk at ~9dkh and Ca at ~430ppm with standard two part dosing.

How would you get 100 ppm swings in magnesium? Its depletion is on the order of 1 ppm per day or less.

 

[donnievaz]

I have the exact opposite problem. As soon as i start getting over 8, SPS start crapping out. Ususally birdsnest is the first indicator for me that there's a problem.

 

[jeff howard]

the key is stability more than the number from what i have seen. falling dkh has caused me problems every time i have messed up and let it happen. the other numbers matter for overall growth and health, but aren't deadly. dkh is outright deadly if it drops, and we aren't talking much.

 

[erk]

How would you get 100 ppm swings in magnesium? Its depletion is on the order of 1 ppm per day or less.

This would be over a week or two. I dose 10ml of ESV Mg a day to keep it stable at ~1400ppm. In a 25 gal tank, that is about 3ppm a day. I don't know why I get such high depletion, but I always have. Maybe it's the salt I use. If I drop below 1300ppm, my hard corals get upset and slowly fade away. Lost a lot of corals figuring this lesson out. Now I just stick with it and it works well.

Edit: I should say that I use Brightwell's salt. I tried Red Sea, but still had high Mg depletion. Add the high alk levels and low nutrient levels, and it became too much for me to keep up with. I don't have a lot of equipment running in my tank. Heater, skimmer, and circulation pumps. No reactors at all. I do have a lot of coraline growth.

 

[gregkn73]

How would you get 100 ppm swings in magnesium? Its depletion is on the order of 1 ppm per day or less.

I always wonder why i add ,as much mg ,as ca. I thing that this is because I use NSW, but I can not find the reasoning of that.

 

[McGee]

What test kit is every one using?

 

[Cory]

I would say its not the alkalinity but the subsequent ph of the swing that gives reefkeepers problems with corals.

Going from 7dkh to 10dkh in 1 hour may not change ph much with sodium bicarbonate, but try that with calcium hydroxide and your in trouble!

 

[Randy Holmes-Farley Verified Community Expert]

This would be over a week or two. I dose 10ml of ESV Mg a day to keep it stable at ~1400ppm. In a 25 gal tank, that is about 3ppm a day. I don't know why I get such high depletion, but I always have. Maybe it's the salt I use. If I drop below 1300ppm, my hard corals get upset and slowly fade away. Lost a lot of corals figuring this lesson out. Now I just stick with it and it works well.

Edit: I should say that I use Brightwell's salt. I tried Red Sea, but still had high Mg depletion. Add the high alk levels and low nutrient levels, and it became too much for me to keep up with. I don't have a lot of equipment running in my tank. Heater, skimmer, and circulation pumps. No reactors at all. I do have a lot of coraline growth.

Well, I can't really see how 1300 ppm magnesium would itself be an issue since that is actually slightly above natural seawater levels. I do think the drop may be due to water changes if your mix does not have that much at the salinity you use.

 

[erk]

Well, I can't really see how 1300 ppm magnesium would itself be an issue since that is actually slightly above natural seawater levels. I do think the drop may be due to water changes if your mix does not have that much at the salinity you use.

I agree that doing a WC would cause a significant drop, but I even get a decent drop when I don't do WCs for awhile. I have no scale deposits on my equipment. Maybe I just need to let it fall down to NSW levels and let the corals get used to it. Maybe drop it very very slowly over the course of several months.

 

[Cory]

I agree that doing a WC would cause a significant drop, but I even get a decent drop when I don't do WCs for awhile. I have no scale deposits on my equipment. Maybe I just need to let it fall down to NSW levels and let the corals get used to it. Maybe drop it very very slowly over the course of several months.

Which test kit? Not all test kits have an accuracy to detect these drops. Randy wrote in his article iorc, that the biggest consumer of magnesium is coraline algae. Which can be as much as 1% by weight. Lots of corraline growth?

 

[Larry L]

I find that alk stability is important, but that Mg is the key to that stability.

This is important - if your magnesium is low and calcium is high, then when you add your alkalinity supplement it will probably just precipitate out as calcium carbonate. Having sufficient magnesium helps prevents that precipitation.

Randy Holmes-Farley has (as usual) a really good article here: http://www.advancedaquarist.com/2002/3/chemistry

 

[erk]

Which test kit? Not all test kits have an accuracy to detect these drops. Randy wrote in his article iorc, that the biggest consumer of magnesium is coraline algae. Which can be as much as 1% by weight. Lots of corraline growth?

I use Red Sea and have been for a very long time. I have checked it's accuracy and it is correct. And yes, I have lots of coralline growth. I also saw an article that gorgonians are also large users of Mg, which I have several that are of decent size and constantly growing.

 

[120reefkeeper]

I agree with an earlier statement that IMHO an alkalinity spike is more of an issue than a gradual fall in alkalinity.

 

[jeff howard]

I lost a good portion of our Satosa when I let my ESV alk run out. There was a water line in the jug and I thought it was fine when it was empty. My PH didnt move much, but I didnt figure it out until my corals started acting stressed. For sure it wasn't related to PH. I dropped a couple points, but not enough to cause it. Though naturally all of them changed when the alk ran out. Was it the alk alone, or a combination of it all? Not sure, but I can say a missed step with alk threw my tank for a loop. Then there was the time I changed from DIY two part to B-ionic, and the change cause me problems. I have just noticed a direct relationship between alk issues and losing SPS. We use Red Sea kits, except for phosphate where I use a Hanna meter. I think we can all agree that keeping it all nice and even is vital.

 

[Myka]

In fact alk of natural seawater is quite exactly 6.5

Most text describes natural seawater in the reef zones to be 7.0-7.1 dKH. I've not actually seen any text describing alkalinity as low as 6.5 dKH before - I can't find this info searching for Millero either. Where did you find it?

 

[Randy Holmes-Farley Verified Community Expert]

I use Red Sea and have been for a very long time. I have checked it's accuracy and it is correct. And yes, I have lots of coralline growth. I also saw an article that gorgonians are also large users of Mg, which I have several that are of decent size and constantly growing.

It might be accurate, but how did you check it?

I don't believe your tank uses more than 2-3 ppm magnesium per day max. I'm not convinced most gorgonia are high users of magnesium (despite their skeletons being made of "high-magnesium calcite") just because they do not deposit a lot of skeletal material. Typical skeleton ratios of magnesium to calcium in such gorgonia are 0.05 to 0.1 ppm (see link below), which is not higher than coralline algae. To drop 3 ppm per day with one of these at 0.1, you'd need to see a drop of 30 ppm per day calcium and 4 dKH per day alkalinity. Same for a typical coralline algae.

https://www.researchgate.net/profil...7006da4dcef000000.pdf?origin=publication_list

 

[Randy Holmes-Farley Verified Community Expert]

Most text describes natural seawater in the reef zones to be 7.0-7.1 dKH. I've not actually seen any text describing alkalinity as low as 6.5 dKH before - I can't find this info searching for Millero either. Where did you find it?

I usually round it off to 7 dKH, but most folks, including Millero in "Chemical oceanography" give values more like the mid 6's dKH. It obviously varies with salinity in NSW, as well as other factors such as location (upwelling, etc.)

 

[Myka]

I usually round it off to 7 dKH, but most folks, including Millero in "Chemical oceanography" give values more like the mid 6's dKH. It obviously varies with salinity in NSW, as well as other factors such as location (upwelling, etc.)

Yeah, I found reference to that text, but couldn't find the actual text online. So where are you rounding it off from, and why would you do that? :mad:

 

[RudyB]

I have a 150gl mixed reef and I have the best results with my Alk at 9 and Cal at 440. What I tend to have problems with is keeping my Mg up. I struggle to keep at 1300 or better. I am trying to figure out what could be causing my Mg to keep dropping.

 

[RudyB]

I have seen this in several areas but just in case here it is. What most people refer to as proper levels.