Having trouble with alkalinity level and evaporation...need advice

[rampro6698]

Sorry, I posted this in the large aquarium section as well but have not heard from anyone so I thought I would give it a try here:

I have a large 600 gal display tank and a total volume of about 750-800 gallons for the whole system. My system is running pretty stable right now with the following water parameters:

S.G. 1.024
dKH 8-8.3
Ca 420-430
Mg 1280-1300
pH 8.23 day and 8.15 at night
PO4 0.006 t0 0.021 (measured by Hanna ULR phosphorus checker)
Nitrates and nitrites undetectable (measured by Elos liquid test kits)
temp 76-78 F

My evaporation rate is about 7 to 7.5 gallons per day. So I am running a Ca reactor with effluent pH at about 6.7 at a steady fast drip and I have a Kalkwasser reactor (Precision Marine) that gets fed by an RO tank and uses a Liter Meter III dosing pump to put 28 Liters of mixed Kalk water into the sump per day. This is all fine except my tank is fairly empty (fairly small bioload of coral and fish) still and my dKH is getting a little hard to maintain at 8 or above. I can maintain Ca, Mg, and even pH fine but my alkalinity will likely need to be added as a supplement of some kind in the future. But my issue is that my kalk reactor is essentially putting in all my evaporation right now as RO water. If I increase the kalk reactor any more (to increase alkalinity) then I will eventually see a drop in SG due to more RO water going into the sump than is evaporating.

I realize all is good and stable right now. But my concern is when I start adding a lot more corals to the tank how will I keep my alkalinity up? I can't use an alkalinity solution because those are made with RO water which is just adding more non-salt water to the sump. I had thought about just running the kalk reactor from the sump itself which would work except I suspect the salt water would precipitate Ca out in the kalk reactor once it is added to that high pH environment. Do you see my concern? Does anyone else have this problem and any thoughts on solutions?

thanks,

Steve

 

[Randy Holmes-Farley]

Correct that you do not want to add more limewater than the evaporation rate, but folks using this combo usually use the CaCO3/CO2 reactor to add the bulk of the alk and calcium.

Can you just tweak it to add more when the time comes? lowering the reactor pH or increasing the flow rate through it.

I'm also not convinced that most limewater reactors produce saturated limewater, but if you are stirring it all the time, that may be all it can accomplish.

 

[rampro6698]

Correct that you do not want to add more limewater than the evaporation rate, but folks using this combo usually use the CaCO3/CO2 reactor to add the bulk of the alk and calcium.

Can you just tweak it to add more when the time comes? lowering the reactor pH or increasing the flow rate through it.

I'm also not convinced that most limewater reactors produce saturated limewater, but if you are stirring it all the time, that may be all it can accomplish.

I only have the Ca reactor half full with ARM Ca media. The reactor is big (8-9" diameter and about 30" tall) so I can probably just add media to get it full and it would do all I need it too. I will try that and try reducing the effluent to 6.5 and continue testing. The effluent from the kalk reactor does check out at pH of 12.3 to 12.5 at various times during the day (I have measured it with a pH probe) so I know it is getting mixed well, etc. It's probably just the Ca reactor not having enough media in it.

 

[Randy Holmes-Farley]

It may be saturated, but pH is a crude measure. A pH of 12.54 at 25 deg C is saturated, but pH 12.24 at the same temp would only be 50% potency.

That said, I'd add the extra media, increase the flow rate, or decrease the pH in the reactor (or some combination of those) if alkalinity begins to decline.

 

[rampro6698]

Very much appreciate your advice!! I will do that. I am learning something new everyday in this hobby. I initially had the reactor half full because I had been doing that for a while and it was meeting the demands fine even at a pH of 6.9 to 7.0 for the effluent. I guess I just hadn't realized that the inhabitants of the tank were demanding more over the last several months as the tank continues to mature.

Thanks again!

 

[rampro6698]

Correct that you do not want to add more limewater than the evaporation rate, but folks using this combo usually use the CaCO3/CO2 reactor to add the bulk of the alk and calcium.

Can you just tweak it to add more when the time comes? lowering the reactor pH or increasing the flow rate through it.

I'm also not convinced that most limewater reactors produce saturated limewater, but if you are stirring it all the time, that may be all it can accomplish.

Could I ask your opinion on something a little unrelated? I have a 100 gal refugium with chaetomorpha and a 6" deep sand bed. But there are two separate parts of the refugium that are empty (just bare bottom). Would it be good to put some live rock in those areas or somehow use them for something? Just seems like they are wasted space. It's all the same water going over these three areas, but only the center compartment (the largest) has the macro algae and sand bed. I do have about 700-750 lbs of live rock in the main display as it is. And if I were to add some live rock in these areas, should I get new (sterile) rock or should I get live rock that already has been colonized, etc. If I use matured live rock with coralline algae and bacteria colonies on it, should I dip the rock to minimize pests coming into the system?

 

[Randy Holmes-Farley]

FWIW, I had an extra refugium filled with live rock that I just decided to remove. I think the detritus collecting under the rock displaced any advantage the live rock itself played in nutrient reduction. It had other uses, such as smoothing out pH and temperature and otehr changes by adding water volume, etc., but I didn't think it was a net benefit worthy of the cost of heating that much water against the cool temps in my basement.