Help. Massive alk drop

[Monkeyfish]

Tank info - 75g SPS dominated. HOB skimmer (Octopus 800s), HOB fuge, Vortech 20, dual media reactor for carbon and GFO, about 65lbs rock and 20lbs sand. Tank has been running for almost 19 months. Other than corals there are 4 fish in the tank: perc, gramma, tailspot blennie and yellow head jawfish. A few shrimp and snails.

Mag - 1300
Calc - 370
SG - 1.025

The probem is that the Alkalinity is all over the place. I stopped testing for about 6 months. Tested about 2 months ago and the alk was 3! Using baking soda and kalkwasser I slowly brought it back up to 8 and cut back on the dosing only to have the alk drop to 5. I stepped up the alk buffering and the alk went up to 9.2 after two weeks. I stopped buffering for one night and the alk dropped to 5.5. I tested twice and tested other tanks which all tested okay; 7-9. A lot of the corals have lost color and one bleached.

What do I do? Why is the alk dropping so quickly?
Any help would be greatly appreciated.

[bertoni]

Many tanks consume 2-3 dKH of alkalinity per day. The tank probably needs daily dosing.

[Monkeyfish]

Thank you for the response. I knew I might need to dose daily, but hadn't realized that the alk could be depleted so quickly.

Would I be better off using baking soda as a daily additive (currently using two teaspoonfuls mixed in 8 oz of RODI water) or kalkwasser as top off?

[power boat jim]

If it is dropping that much day to day give some thought to getting a Ca reactor.

[Monkeyfish]

If it is dropping that much day to day give some thought to getting a Ca reactor.

Unfortunately, even if I had room for it (which I don't), I don't have the $ right now. :(

[cthedaytrader]

Have thought about BRS doser?

Much cheaper than a Ca setup. If you have a controller you can use that to dose daily if not you can use a timer.

I use two BRS dosers with my apex and it works great.

Still have to dial it to match tank demands but easier than manual dosing especially with a high demand tank.

On my tank which uses about 150ml a day of each two part now to maintain alk, it makes it much easier and more stable to dose as I spread them out over the whole 24hours.

[Monkeyfish]

Thanks C. I'll have to check it out.

[m2434]

Do you have a lot of stony corals and/or coralline algae? If so, could definitely be the cause.

As to what to do, I'm not sure a BRS doser is cheaper than a CA reactor in the long term. Although, Ca reactors seem like a PITA, to dial in and the potential pH problems. How much evaporation do you get daily? You could use kalk, it is pretty reasonably priced, but your limited by evaporation. Personally, I use vinager to supersaturate kalk, and then manually dose some 2-part to top it off. This method works well and is fairly effective. You probably don't want to go the vinager route though, unless you specifically want to dose vinager, as I do.

[chuckreef]

Thank you for the response. I knew I might need to dose daily, but hadn't realized that the alk could be depleted so quickly.

Would I be better off using baking soda as a daily additive (currently using two teaspoonfuls mixed in 8 oz of RODI water) or kalkwasser as top off?

1. There is no "might" about it, in an sps tank one must supplement alk daily.

2. Not sure ... better off than what? Yes, baking soda is the "best" choice in terms of chemical dosing regimes if one looks just at alkalinty and relative safety/stability.

I recommend you either prepare a gallon of two part solution per one of the recipes or buy a gallon of pre-made two-part immediately; and begin manual, daily dosing until you can research, choose and implement a permanent calcium and alkalinity maintenance regime.

[bertoni]

I agree that a 2-part, either a commercial one or the DIY version, is an easy way to get started. That's what I'd do.

[Monkeyfish]

I was using a 2 part, but the calc was getting used way more than the alk buffer so I switched to baking soda and Kent Turbo calcium. My problems seemed to have started when I began chasing numbers and tried to get my parameters where they "should" be. My corals looked a lot better when the dkh was 3!

I'll just have to continue playing with it until I figure out the correct amount of each buffer required to maintain the chemistry at a consistent level.

[bertoni]

If the corals looked better with the dKH at three, I suspect the test kit is having trouble.

[power boat jim]

If the corals looked better with the dKH at three, I suspect the test kit is having trouble.

That^^^^ or are you sure its not MEQ/L? usually anytime dkh starts to get 4 or less really bad things start to happen.

[Monkeyfish]

I'm using Salifert tests. Don't think it's the test kit or meq confusion, but I'll double check (again) when I get home tonight.

Maybe I'll purchase a new test kit just to be sure.