Correlation of Alkalinity and Nutrients (N and P) From My Experience

Earl Karl

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Unfortunately, I do not have pictures with results because this was back when I was 15 years old, with no social media accounts, and no knowledge of reef forums. Worst yet, I never had a phone until I became 18 (I'm 20 now). However, I did some experiments back in the day and it all started with one chart from Red Sea that my friend showed me.

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Majority of us know that Alkalinity correlates with skeleton growth and Nitrogen and Phosphorus correlates with tissue growth as they are part of the building blocks of life (along with Carbon). However, not many people know about proper ratios, which is important for the pace of skeleton growth in conjunction with tissue growth. Doesn't mean you can't have success without knowing this, but results can be more prominent when you apply those ratios the proper way.

Many people keep Alk. at around 8, and high nutrients like 0.08 ppm PO4 and 10 ppm NO3 (yes that is high!). At best they get sufficient growth, but I want the best of the best for my animals.

I started my first acro growout tank (DIY 48x24x12, 60g) with 12 dkH, 0.1 ppm PO4, and 2 ppm NO3. No protein skimmer, just a refugium that had a volume of 10% of the display with a return pump that gave 10x turnover. I did water changes or dosed KNO3:KPO4 in a 16:1 ratio depending on NO3 and PO4 levels. Used a Korallin CaRX with TLF Reborn with occasional Kalk to supply Ca and Alk. and maintain optimal pH. Dosed Seachem Potassium, Magnesium, Strontium, Iron, Reef Plus, Lugol's , and TLF Acropower every Tuesday and Saturday using recommended dosage. Broadcasted zooplankton every night. PAR was 400-500, close to evenly distributed with 3 EM Radion XR15 Pro Gen 3 hung up pretty high. Flow was achieved using 2 VorTechs MP40s, giving me about 60 times turnover (70x in total with the return). The acros grown was Oregon Tort (Acropora Tortuosa), SC OP (Acropora Tenuis), and Strawberry Shortcake (Acropora Microclados). All started at 1". There was only one fish which was a Splendid Pencil Wrasse (Pseudojuloides Splendens).

Growth was slow at the beginning, but after first month, I had insane growth. I was getting 2-3 inches depending on species per month. However, color was dull. Oregon Tort was like dirty purple. SC OP was dark turquoise with dark orange polyps. SSC was brownish green with dirty pink corallites. After 5 months, the Oregon Tort was growing out of the water and the acros were almost touching. So I trimmed them and started lowering parameters very slowly by lowering dosage and effluent output each week until I got 7 dkH, 0.01 PO4, and >1 NO3. Took about a month. Then it took another few months for my acros to finally color up. Coral growth was almost halted under these parameters, but the color was amazing.

Then I wondered, what if I went with the middle? So I started a new experiment, same as above but now with two tanks (taller this time, 18" height). One tank has the method I have explained above. The other tank was just going to a consistent 9.25 dkH, 0.05-0.08 ppm PO4 and 1 ppm NO3.

Tank with 9.25 dkH grew half as the 12-7 dkH tank with only growing around 1, maybe 2, inches per month. However, acros in 9.25 dkH had MUCH better coloring, almost as good as 7 dkH, but not amazing. By 5-6 months when the acros in the 12-7 dkH tank got around the 12 inch mark, I started to lower parameters. Took another few months til the acros to color up nicely. However, there was a twist.

By the time the acros in the 12-7 dkH tank colored up, the acros in the 9.25 dkH grew MORE by then, with nice coloration as mentioned previously (not as good as 7dkH though).

The 12-7 dkH method is a great method for someone who wants a well established reef display fast, while the 9.25 dkH method is great for someone who does aquaculture and/or has a fragging business.

The biggest difficulty of this experiment was maintaining optimal NO3 and PO4 levels. This tends to be a common issue with a lot of reefers.

Lower Alk. is only better for low nutrient tanks. As I mentioned, nutrients correlate to tissue growth while alkalinity correlates to skeleton growth. In low nutrient tanks, high alkalinity will cause the skeleton to grow faster than the tissue, resulting in burnt tips in mainly acros. With low Alk., you won't get the growth, but you will have amazing colors. This is more catered to fully matured reef packed with colonies.

However, people with high Alk. can combat low nutrients (in most cases from nutrient export doing too much) with broadcasting any form of zooplankton every night. That is somewhat how the ocean works as well. Despite very low nutrients in NSW, corals consume zooplankton (not as much as you think though), during night to compensate for nutrients (N and P). However, NSW's Alk. is at 7, so low nutrients is not a big deal in the ocean. Tanks with higher dkH and lower nutrients will definitely benefit from feeding.

In higher nutrient tanks, lower alkalinity would create poor coloration with poor growth. With higher alkalinity along with higher nutrients, both can keep up with each other's pace resulting in much faster tissue and skeleton growth, however, due to higher nutrients, you won't get those amazing colors. More catered to frags that you just want to grow out fast as possible.

In conclusion, applying proper ratios of nutrients and elements can result in more prominent success. My new acro growout build will go with the 9.25 dkH method just because stability is key and the fact that I will be fragging a lot in this tank.

Thank you Earl and Karl who made this experiment possible.
 
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hotdrop

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That kind of matches my experience so far, at least for phosphate. The Nitrates vary so wildly and drop down to 0 so quickly I don't even know when to measure them to get accurate comparisons or If I should be manually dosing.
 

blasterman

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Only caveat I have is the high dKH number.

High bicarb levels without correspondingly adequately high pH results in hard corals that can't adequately form calcium carbonate. All, and I repeat all of my big SPS buddies have been running dKH lower and lower over the years irregardless of nutrient levels.
 

Mykawl

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What ratios would you suggest with ease in mind, so if nitrate kept under 5 ppm, phosphate kept under .1 alkalinity 8 and slightly elevated mag/cal
 
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Earl Karl

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That kind of matches my experience so far, at least for phosphate. The Nitrates vary so wildly and drop down to 0 so quickly I don't even know when to measure them to get accurate comparisons or If I should be manually dosing.
Nitrates will go up and down like crazy, especially if you're like me and have a giant refugium while putting a lot of food into the tank. I dose reef roids and it brings my nitrates up. But during my experiment back then, I only had one fish in there and all he ate was ghost shrimp. So I used KNO3 and KH2PO4 (you can buy these in bulk for very cheap, like $3 a pound or something), there is a calculator that tells you how much to dose to get the desired level. I adjusted levels first, then I continuously dosed in 10:1 ratio.

In your case, if you're getting algae growth and you still get zero ppm NO3, DON'T dose. Hobby grade test kits WILL lie to you and/or isn't able to read low, NO3 is present if algae is present since algae need nutrients to grow. If not and your corals are starting to pale, either feed more or start dosing nutrients. I prefer dosing nutrients since it is more controlled, but could add more complications. Feeding is an easier alternative. I'm crazy enough to weigh my food.
 
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Earl Karl

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Only caveat I have is the high dKH number.

High bicarb levels without correspondingly adequately high pH results in hard corals that can't adequately form calcium carbonate. All, and I repeat all of my big SPS buddies have been running dKH lower and lower over the years irregardless of nutrient levels.
Of course pH has also a big role in skeleton growth, which I forgot to mention. However, I ran Kalkwasser (with a CaRX), a giant refugium, and again I forgot to mention, a cheap ozone setup, for me to achieve optimal pH (which I did mention), so it was never really important for me.

Alk. and pH does have correlation, the more an Alk. source is dosed, usually the higher the pH, especially true with Kalk. However, this doesn't last forever as the outside environment filled with CO2 can drive pH down due to H2O + CO2 -> H2CO3 (carbonic acid) being formed.

Also, when using an Alk. source like NaHCO3 (sodium bicarbonate) along with CaCl2 (calcium chloride), the NaHCO3 and CaCl2 will disassociate in water into spectator ions which is Na, HCO3, Ca, and Cl. The coral will use Ca and HCO3, leaving the byproduct NaCl. However, since HCO3 can't be used to build CaCO3 (Calcium Carbonate), the coral has to pump out the H+ out of HCO3 to form CO3 (carbonate), so it can be usable for their skeleton. However, you are also left with H+ and H+ is literally acid, which will bring pH down as with H2O, it forms H3O. This is why you hear people having pH problems. Initially you will get a bit of rise in pH (unless you're already at 8.3 or higher since the pH of NaHCO3 solution is 8.3), but after the coral processes the HCO3, pH will drop. Even when using NaCO3 (Sodium Carbonate), you still have to deal with the CO2 forming with H2O.

This is why I use Kalk along with CaRX, ozone, and a refugium as it gets pH to optimal level, not too high or low.

There are many ways to be successful, as success is subjective. However, which method is best for the coral on the other hand, that we can debate on.
 
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Earl Karl

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What ratios would you suggest with ease in mind, so if nitrate kept under 5 ppm, phosphate kept under .1 alkalinity 8 and slightly elevated mag/cal
There are Ca and Alk. balance calculators out there, type in your desired Alk. and you should get your balanced calcium. Having elevated Ca with an Alk. of 8 dkH may cause stability issue.

Also, with an Alk. of 8 dkH I would run lower nutrients, NO3 at 0.5-1 ppm and PO4 at 0.03-0.06 ppm, depending on 16:1 N to P ratio.
 
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Mykawl

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There are Ca and Alk. balance calculators out there, type in your desired Alk. and you should get your balanced calcium. Having elevated Ca with an Alk. of 8 dkH may cause stability issue.

Also, with an Alk. of 8 dkH I would run lower nutrients, NO3 at 0.5-1 ppm and PO4 at 0.03-0.6 ppm, depending on 16:1 N to P ratio.
Big thanks will look further into this
 

Bahadir_S

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new to reefing hobby.
thanks for sharing your experience. That's good example for controlled experiment.
What about LPS dominated tanks? Can we use the same approach for LPS corals?
 

rq786

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Thanks for the great article
In your 9.25 dkH experiment what level you kept for CA and Mag
 
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Earl Karl

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Thanks for the great article
In your 9.25 dkH experiment what level you kept for CA and Mag
There is a calculator online where you can calculate balanced Ca and Alk. levels. At 9.25, I keep it at around 425 ppm. Mag I like to keep it high as it helps with stability, around 1400 ppm. No lower than 1350.
 

Randy Holmes-Farley

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Thanks for the great article
In your 9.25 dkH experiment what level you kept for CA and Mag

IMO, calcium levels are not that important as long as they are in the 400-550 ppm range. I do not see a reason to alter either calcium or magnesium optimal levels based on the actual alkalinity. I would target them all independently to optimal ranges.
 
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Earl Karl

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IMO, calcium levels are not that important as long as they are in the 400-550 ppm range. I do not see a reason to alter either calcium or magnesium optimal levels based on the actual alkalinity. I would target them all independently to optimal ranges.
Agreed, as long as the Alk. is stable, no need to chase numbers.
 

jRatanak

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Super interesting to read! However as someone with higher N and P levels, and a moderate Alk, would it likely be more effective to slowly raise Alk for better N and P utilization, or maintain a stable Alk and try to adjust N and P accordingly? I have a feeling I know the answer, but would definitely appreciate some input!
 
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Earl Karl

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Super interesting to read! However as someone with higher N and P levels, and a moderate Alk, would it likely be more effective to slowly raise Alk for better N and P utilization, or maintain a stable Alk and try to adjust N and P accordingly? I have a feeling I know the answer, but would definitely appreciate some input!
Really depends on what you are trying to achieve. If you want fast growth, raise your alk. slowly. If you want good color, lower your nutrients and alk. slowly. If you want the happy medium, lower the nutrient levels a bit. Most importantly, keep nutrients balanced, your NO3 should be 10.5x the PO4 to achieve 16:1 ratio.

Remember to keep pH at optimal levels, corals can't utilize CO3 (alk.) as well when pH is low.
 

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