calcium consumption stopped, alkalinity consumption increased, and algae growth

RLHam3

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Greetings! I’m generally just a lurker, and I don’t usually post. But I’ve run into an issue that I’m not sure how to handle, and I wanted to see if the crowd here might have some good ideas.


Background
I have a 75 gal reef tank (probably around 80 gallons total volume). The tank has been running for about a year and a half. I use red sea pro salt, and do a 15 gal water change every 2 weeks. I mainly have it stocked with LPS and SPS . The tank has a pretty light bioload with 1 yellow mimic tang, 1 firefin tomini, 1 leopard wrasse and 1 social fairy wrasse (plus CUC). Up until recently, I have been dosing 25 ml of all-for-reef on a daily basis, with a 2.5 ml of seachem fusion 2 in addition. I also have been dosing Brightwell magnesium P as needed (usually every 1-2 weeks). I make my own RO/DI water. TDS is reading 0.0 on the product water.


Here are my most recent parameters:

Salinity - 1.026 (refractometer)
Nitrate – 0.5 (Hannah) – a bit lower than usual
Phosphate – 0.06 (Hannah)
pH – 8.2 (salifert)
Calcium – 520 (Hannah)
Magnesium 1440 (red sea pro)
Alk – please read further (tested using Hannah)

The first year has of course had its ups and downs, but the tank has been stable. All of the corals have been growing well, and the rocks all have a layer of coralline algae. The back wall of the tank also had a coating of coralline algae up until recently.


Current Situation
About a month ago, I noticed that the coralline on my back glass looked like it was starting to be covered by a green/brown algae(see attached). Around this time, I also noticed that the algae forming on my glass started forming much faster. For the first year or so, I only had to magnet the glass off once a week or so. I am now having to do it almost daily?

Around this same time, I also noticed that my overflow box had a lot of bubble algae inside of it. I had not noticed the algae before, and it was a large amount. I resolved to try to remove it manually. I closed the drain valves to hold everything in the overflow box, and manually removed as much as I could. I then filled the box with RO water and siphoned it out several times over. I now have a light-proof lid to prevent any future growth there.

(I know that this is not the perfect removal method, but that’s not what I’m here to talk about today... I think?)


After this, I didn’t notice any change in nitrates/phosphates, but I did notice that hair algae started growing on my glass. It seemed to mainly be growing just under the water surface, where my magnet wouldn’t reach. I let it grow for a bit, but when It got longer, I removed it with a razor. Since then, I have not noticed any other excess algae growth, except for the algae overtaking the coralline on the back glass.


This was about 2 weeks ago. When I removed the hair algae, I noticed that my calcium consumption seemed to have completely halted. I didn’t notice this at first, so I kept doing the All-For-Reef. I first noticed an issue with my alk dropping faster than normal. I then tested, and saw that the calcium was higher than usual(a bit over 500). It has generally been maintaining at 425-450 since the tank went up. When I noticed it was high, I just decided to skip a day of dosing. The next night when I tested the calcium was at the same level, but the alk had dropped significantly. While the alk has always been fairly stable up until now, it dropped from 8.9 to 7.7 within 24 hours.

Up until this point, a single daily dose of All-For-Reef combined with seachem fusion 2 was enough to keep alk stable for the whole day. Since then, i have stopped dosing all-for-reef. I have continued dosing the fusion 2, but I am now having to dose 18 ml a day when I used to only be 2.5 (plus all-for-reef). Seems like a lot to me, and it seems like a huge decrease in kh in a short amount of time?


The Question
This seemed odd to me. Why would calcium consumption stop, while alk consumption accelerated? The corals don't appear to be suffering yet, but I’m not sure if I’m seeing much/any growth. Checking it last night, the calcium was still elevated at 518, while the alk keeps bouncing up and down between doses. I aim to keep it at 9 if possible.

I'm worried because I have always dosed fairly equal parts of calcium vs alk, and the parameters have always been fairly stable. It seems weird that my tank just suddenly stopped consuming calcium. Does this mean that the corals are no longer uptaking calcium and thus no longer growing? No changes to flow or lighting within this time.

And also, what is this algae on my back wall? (see pic) And what do I need to do to get rid of this so I can make room for more coralline growth?

1.jpg 2.jpg 3.jpg
 
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RLHam3

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Thanks for the quick response here! And those were my thoughts too which is why I'm so confused?

The only things I've added to the tank in the past couple of weeks are: fusion 2, food (reef chili, rod's and lrs), red sea AB+ and seachem zoo/phytoplankton. I did also dose twice from one-year-old bottle of microbacter 7 after this started. No water change yet. I change the filter socks every 3 days religiously.

To my knowledge, none of this should have this effect? What would deplete alk like that? I'm finding that I have to dose 3-6 times a day now to keep alk stableish in the upper 8s

And that is absolutely a good thought about the test kits too. I have been testing calcium and alk with my salifert kits, and have been getting consistent reports there too?
 
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RLHam3

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Bump(Please help!)

Last night the calcium was still at 495.

I am starting to notice some favias, micromussa, pectinia, and chalices that are receeding. And I see their white Skeletons on some edges
 

killer2001

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The calcium intake slowing down appears to be the result of the green algae taking over the coraline algae.

Do you carbon dose? Perhaps, this green algae is consuming nitrates before carbon dosing is able to achieve any +alk gains.
 

Randy Holmes-Farley

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Carbon dosing in a sense of promoting the denitrification process.

He doesn't seem to suggest a big drop in nitrate, which is currently at 0.5 ppm. Alk may have risen if there was a big drop in nitrate to that point ( a drop from 50 ppm would add about 2.3 dKH), but at that current nitrate level, the nitrogen cycle is not, at the moment, appreciably adding or depleting alk.
 

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