Coral/coralline won’t grow, need help

[Tom-Nanoreef]

A year ago, I set up a 15 gallon tank with plenty of live rock and had healthy coral and coralline growth. After a few months, I neglected my tank and much of my previous coral died. In January, I decided to restart the hobby and started up again. I made some rash dosing mistakes, but since January, none of the coral in my tank has lived and my corraline has died a lot. My parameters have been relatively stable other than 0.3-0.5 max changes every week, my lights have not changed and should not be the issue, and I see no pests eating my coral. The only issue that I have is a cyano bacteria infestation that I am working on. My hermit crabs are happy and healthy, so are my fish. Realized my water change water had much lower alkalinity than main water and have started dosing it, but I have been changing water weekly for months now. I had 2 mushrooms that died recently with at most 0.3 alkalinity swings per week (water changes), though seemingly unlikely.

 

 

Tank setup:

Coralife LED Biocube 16 gallon

Back chamber - Bio balls in the back chamber, chaero refuge, a lot of rock and sand (Not sure about specifics), Seachem phosguard and matrixcarbon (removed a few weeks ago after being advised), a powerhead, and a heater

 

Parameters current:

Alkalinity - 7.8 

Calcium - 410

Magnesium- 1250

Salinity - 1.025

Ph - 8

Nitrates - 0 (last I checked)

Heat - 78 degrees F

 

 

[Tired]

You likely don't have enough nutrients. You want to have a minimum of 0.03ppm phosphates (get an accurate kit and test it) and 5ppm nitrates. Your weekly water changes are probably what's causing that. Stop doing water changes until something absolutely needs to be replaced or removed, and remove any filter media that absorbs nutrients. Alternately, dose nutrients. Either way, consider feeding your corals directly, and make sure your fish and other critters are getting nice meals. Fish should eat at least once daily, if not more often.

 

For the cyano, just use a turkey baster or pipette to blow it off any corals it grows onto. If you use pure water, stock an appropriate cleanup crew, and provide enough nutrients to let algae grow, the cyano should go away on its own. 

[Tom-Nanoreef]

Would this explain the lack of coralline growth? I have always thought that my alkalinity was the issue, do you know how much alkalinity swing corals/coralline can live with for reference? Thank you for your help, I appreciate it.

[Tom-Nanoreef]

This is the only coral I have left, GSP and barely hanging on.

[Tired]

I don't know exact numbers on the alk, but I do know that, for most parameters, stable is better than unstable and chasing a goal. Dosing is only helpful if it moves the parameter to a good level and keeps it there. If dosing just causes the level to swing, it's likely to do more harm than good.