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Case of the disappearing alk


Bpb

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So I've been having an alkalinity issue fairly suddenly. Tank is a 1.25 year old 55 gallon mixed tank with about 20 or so sps frags/colonies ranging from grape sized to saucer sized and. My method of calcium and alkalinity supplementation since January has been kalkwasser added in my ATO. About a month ago I reached full saturation to keep up with the steady demand. Bi weekly water changes of 10%. I test frequently. At least once a week. All tests are done with Red Sea pro test kits and a calibrated refractometer

Over the last 8-9 months I've run a bit lower salinity, to save a bit on salt for water changes, and just making up the difference with kalkwasser. Here come a few changes I've made in the last month, and my result has been plummeting alkalinity.

First, I started feeding more filter feeder type stuff. I feed my tank fairly heavily as it is. 1/2 cube of non-rinsed PE mysis 3x a week. Two pinches of NLS Thera+ pellets daily, and every other day i feed a mixture of reef chili and seachem Zooplankton. I like to feed. I change my gfo and carbon reactor media regularly. My nitrates are always testing undetectable and nuisance algae isn't much concern.

Well ever since I got on the reef chili and zooplankton, my sps have shown a noticeable improvement in growth and color as to compared to before. Two thumbs up.

Secondly I took the last two weeks to bump my salinity from 1.022 to 1.026. I did this by only using 1.026 water in my ATO and no kalk. Since I've reached my target I've been back on kalkwasser for two days.

Corals look good, but my alkalinity is falling fast. It was kept steady at 8.5 or so for months, and when I noticed it fall to 7.5 I increased my kalk concentration. Held there and decided to keep it there.

Well ever since I increased my salinity, my calcium is staying at 450 ppm, magnesium at 1360 ppm, but my alkalinity is wanting to dip down to 6 dKH and lower. I've taken to dripping 40 mL of two part alk mix daily to try to get it back up to 7.5 but it just won't make it. Been testing daily for a week.

How are calcium and magnesium not dropping, but alkalinity is dropping g like a sack of potatoes. I mean 40mL should be adding 1 dKH to my tank, and combine that with about a gallon of full strength kalk added a day as well, how am I not keeping up. Are my sps now growing big enough to out compete my ability to supplement with my current method? Seems calcium would be falling too. Sorry for the wall of text. Just trying to answer as many questions as I could think would follow

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I don't have a ph tester actually. I've always just monitored alk. Couldn't tell you what it's currently at. In the past every time I've tested it's been between 8.0 and 8.2 or so.

I've read about super saturating kalk with vinegar, just didn't think it would be necessary so soon. My stony load is not THAT heavy. Maybe my evaporation is down and it's just not adding kalk quite as often.

Still the biggest mystery is why only the alkalinity is dropping. And not the calcium

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You could be right about your coral absorbing your alk and you not able to keep up. I have a friend that had to run a ca reactor and a dosing pump to keep up with the absorption.

Also what test are you using? How old is your test kit ?have you compared with other test kits ? Sometimes you get Bad test kits or they are too old.

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Red Sea pro. About 7-8 months old. Just finished the alk test yesterday. I've got a brand new one ready to go. They've been compared to other kits, tanks, ect and they're good. No funny stuff.

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I could be way off base here. My understanding is alk can drop with higher organics in the water. It sounds like it started really dropping when you increased feedings. The exact same thing happened in my current tank and in my previous tanks that I've fed heavy in. I just dose alk everyday to keep it up since I have some fish that need to be fed frequently. My coral load is very light right now so I know it's not that.

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That's an interesting idea. I know phosphate in the water can precipitate out as calcium phosphate. I started feeding more because my acros were looking so pale and the increased feeding has made them alot better looking. Might just have to think about automating my alk dosing. Calcium reactor not in my future. Way out of budget

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