ALK in an ULNS System

Ashish Patel · Oct 10, 2017

My tank is about 8 months old - tank volume is 135 gallon (overstocked, over fed). Many people suggest for SPS in an ULNS, ALK should be around 7-7.5 DKH and going higher than 8.5 will cause problems. My tank is pretty low on nutrients and I only use cheato, marine pure, miracle mud and a skimmer. Does this mean I have a bigger window for my ALK? I do have a high bio load so nutrients are going into the tank. In past TOTM articles many hobbyist with low nutrients ran 10-11 DKH and grew SPS out of control, the only difference is they used refugiums and not Vodka,

So can you run higher ALK on a system like mine? What are the risk? I feel long term it would be easier to maintain slight higher ALK as most saltmix run 9-10DkH and making even a 20% waterchange increases my alk significantly.

Nitrates (salifert): 0.2 PPM
Phosphates (Hanna ULR) 0.02-0.05 ppm
DKH: 8DKH
CA: 420DKH
MG: 1350-1400

Any suggestions would be appreciated!

Randy Holmes-Farley · Oct 10, 2017

The issue is burnt tips, possibly from skeletons growing faster than the tissue can keep up in a low nutrient situation.

If nitrate is really 0.2 ppm, it is on the low side and I'd be careful to not raise alk too much (7-8 dKH is usually OK).

If you do smaller water changes, there won't be an issue.

20% change with 10 dKH water starting at 7.2 dKH boosts it to 7.8 dKH. Borderline, IMO.

Ashish Patel · Oct 10, 2017

Generally, I do 10-15% waterchange every 2 weeks and this is not so bad. But recently I fear my tank has been poluted and wish I could do a 50% waterchange but instead just ran some new carbon. I am fairly confident my nitrates are 0.2 and perhaps lower. Salifert test kit water comes out almost clear but can pass as 2PPM from the side glass view - divide that by 10 I get 0.2 PPM (estimate but I know its <.5)

I just want as much redunancy in my parameters as possible while obtaining the best health. Running low ALK IMO is harder to maintain with frequent waterchanges and lets say in time something happens where my nitrates jump up. (something dies, autofeeder, tank maturity, etc), What happens when the Nutrients are too high and the Alk is too low?

I will keep my ALK around 8DKH (has been only a few days), I think only time will tell but this seems to be a good number.