Sudden decline of successful reef (monti eating nudis and alk drop)

[frisky_polyp4250]

I have a 25g AIO cube tank that I have had set up for about 6 months. It is lit with an AI prime, and I do a 7g water change w/ rodi water and reef crystals religiously every Sunday. The only fish that I keep in the tank is a small yellow tang (come at me tang police). Up until about 10 days ago, this tank has been an absolute pleasure to maintain and watch all the corals grow without any real problems. Unfortunately, about 10 days ago, I saw my first montipora eating nudi. Every since then, I have been dipping all montiporas in coral rx for 5 minutes followed by a 15 minute dip in revive and then brushing off all eggs I can find on the monitpora. At this point, every montipora is pretty much totally dead, which sucks, but is at least explainable. However, both my hammers and acans are receding and not opening all the way, one of my favia's is bleaching and showing skeleton, my green slimer acro is losing all color, my purple birdsnest isn't opening and looks like is starting to die off, and my orange lepto is bleaching pretty bad as well. I have attached all water testing results since I started recording them in december. As you can see, I noticed my fist nudi on 3/15 and it seems like there was a correlated alkalinity drop around that same time. Could the alk drop from 8.45 to 6.7 and then back up to 8 in about a 10 day period be the only thing that caused all those other corals to be upset? Or is there some other problem lurking in this tank? Also is there anything else that anyone could think of that could be responsible for the sudden decline of the tank as a whole?

Checked my temp graph for this tank it has been consistently hovering between 77.5 and 79 since early february.

-------------PARAMS TIMELINE------------
12/26
Alk: 8.5
Nitrate: 15

1/3
Alk: 8.2
Nitrate: 7
Calcium: 375

1/10
Alk: 8.25
Nitrate: 10

1/20
Alk: 9.3
Nitrate: 10
Calcium: 420

1/26
Alk: 9.1
Nitrate: 10
Calcium: 420

2/2
Alk: 9.75
Nitrate:
Calcium: 460

2/9
Alk: 9.9

2/9
Alk: 9.75

2/23:
Alk: 9.3
Nitrate: 15

2/28:
Alk: 8.9

**Went on vacation and missed a water change

3/9:
Alk: 8.45
Nitrate: 25

3/13:
Alk: 8.45
Nitrate: 6

3/15: Noticed first monti eating nudi

3/21:
Alk: 7.3
Calcium: 420
Magnesium: 1350
Nitrate: 5
Phosphate: .03

3/22:
Alk: 6.7, then dosed 15ml of brs soda ash, and then 7.6 about an hour later
Changed dosing of 2 part from 4mls/ day to 10mls/day

3/23:
Alk: 7.85

3/24:
Alk: 8.15

3/25:
Alk: 8.3
Calcium: 400
Nitrate: 3
Magnesium: 1455
Ammonia: 0
pH: 7.9
Phosphate: .25

 

[laverda]

Corals are definitely sensitive to ALK swings. Especially rapid changes. Hard to say if that is 100% the cause of your issues. I suspect the dipping contributed as well.