Crushed coral and alkalinity

[pwreef]

I decided to replace my sand with crushed coral. I removed the nasty 3-4 year old fine sand (I inherited it from previous tank owner, not knowing any better) that was about 3-inches deep making it not a DSB nor a SSB. I removed all water rocks/animals first and then scooped out the sand. I rinsed crushed coral with tap water until it ran clear. I reused old water, adding about 25% new saltwater to replace. My KH went from 9.5 to 6.7 using Hanna. Needless to say many corals have died. Is there something in this crushed coral that is 'using up' alkalinity? Even now I have to constantly raise the amount of 2-part I am adding to keep KH in the 7.8 range.

 

[bertoni]

The drop in alkalinity might have happened for a number of reasons. It's possible that the surface of the coral acted as nucleation sites for precipitation, or maybe removing the sand cleaned up the water enough that the corals grew faster, for example. Over what kind of time frame did the drop happen?

 

[pwreef]

I tested the next day and compared to the two days before.
Here's my log:
2/16 9.29
2/23 9.40
3/2 8.56
3/9 - removed sand
3/11 6.77 (increased my doser slightly)
3/21 5.57
3/22 5.9
3/24 6.9
3/30 7.4
4/4 7.8
4/14 7.7
4/18 7.8
4/27 7.9
4/30 8.6 - this is odd
What's strange is that now the 2-part dosing timer that I use on Reefkeeper, is set to twice the time that it was before I removed the sand. Perhaps the pump is acting strangely. I use BRS pump. I tested sometime during this incident and the rate seems correct.
Frustrating that I cannot keep it constant.

 

[Randy Holmes-Farley]

I'm not sure why you see the drop you are seeing. Dissolving deep sand can add a little alkalinity over time, but the effect is usually hardly noticeable (and primarily only because the sand may be reduced over long periods).

FWIW, real or error, there are just to many possibilities to worry about what it was actually from. I'd just dose the higher amount now if you are confident in the current test results..

 

[bertoni]

I agree that the cause is a bit mysterious. I would clean the pump and its delivery line, and check for blockage. That kind of problem does show up now and then.

 

[pwreef]

You know I have been reading and thinking that it might be GFO. I had a pretty cool tank with big colonies of orange monti and birds nest that ran fine with just chaeto. Then they all declined. I got tired of orange cap so I just cut it up and got rid of it. I think about the same time I added GFO reactor. My phosphates are about 30 ppb. I have also been reading of anecdotal issues with lower alkalinity because of GFO. I think I am going to take it off line for a little bit and buy some cheap sps frags just to see what happens.

 

[Randy Holmes-Farley]

FWIW, 30 ppb phosphate is plenty for corals. It is more than is normally present in the ocean.

 

[pwreef]

Randy, Thanks a lot for your help! I read your article about critical parameters in reef aquaria and I understand and agree, but fact is I lost some beautiful corals and from what I can tell the tank started declining after I bought the GFO reactor in Sept. Then Christmas time I was away from home and my LED light died, so tank was without proper light for 4 days or so, being lit by a floor lamp that my dad could rig on a timer. I don't know, but something tells me that in the ocean storms happen for more than a few days in a row and light gets very low. Following this some SPS were still alive, but declined steadily. Zoas, acans, palys, LPS like hammer (lost one, one is perfectly fine), branching hammer are doing okay. So I have to do something to get better at this, as I don't feel like giving up the hobby quite yet.

 

[tmz]

30ppb PO4 should be fine. 4 days lights out and/or signifcant drops in alk would be more likely suspects tan gfo ,imo Once sps starts a down spiral it's hard to stop sometimes.