Why wont my Ca & Alk stabilize?

Silverlava

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Hello! I have had a new 90 gallon Redsea Penninsula system running for 2.5 months now and I've never had this much trouble balancing the calcium and alkalinity. I'd love any tips!

I have one other tank (75 gallon system), so I'm targeting the same levels to make maintenance easy. This tank has been running for a year at 10.5 dKH and 410 Ca. The new 90 gallon tank I can't get to stabilize no matter how much I dose.

Monday last week I turned off my autodoser, and measured the drop in levels over 2 days to get a new regular dose. I am dosing on a 24 hr schedule with a redsea dosing head-- Ca doses at the half hour, dKH at the top of the hour into a fast moving section of the sump. (I have not observed precipitation since moving it to this section for dosing.) I brought the levels up through manual dosing to Ca 410 and dKH 10.0. (Mg at 1440, didnt need dosing.) The daily dose is 23 mL Ca, and 35 mL dKH, which is double what I dose on my other fully-stocked 75 gallon system (LPS mostly).

After exactly 3 days with the new autodose level on, the new tank is now 9.1 dKH, 380 Ca, and 1440 Mg. PH is 8.2 ish (measured with API test kit so not super accurate IMO). This new tank is very low stock on corals-- maybe 20 zoa polyps, 2 cynarina, 1 trachyphyllia, an alveopora, a favia (10 polyps), a blasto (4 polyps), a mushroom, a 5-head duncan, a small colony of pulsing xenia, and maybe 5 heads on a clove polyp. Sounds like a lot when I write it, but 90% of the tank is bare rock structure.

Some possible things Im wondering if they affect the levels--
1. We don't have fish in the tank yet. We've been waiting on a custom lid and it has taken forever to ship. Can fish stabilize levels? Or does a lid keep the ca/alk from evaporating out or something?
2. We dont have a skimmer yet -- no real need for one since the waste levels are low. Does a skimmer keep levels stable?
3. We used different sand in this tank vs the other -- this one has carabsea aragonite live sand, and my other tank has a finer particle size on it but i forget what it was called. We are also using a different type of rock in this aquarium vs the other. 1st tank is marcorock new tank is a smoother composite rock. The smoother rock sat in our first tank's sump for 3 months though, so it was live when it went into the new tank.
5. The tank is next to a window, but it only gets direct light for 30 mins in the late afternoon due to the roof angle & tons of trees-- no issues with algae yet. But we'll get a curtain if we need to. Not sur if light could cause issues though
6. Our other tank doses hourly during the daytime only, controlled by an apex. Should I adjust the dosing schedule on the new redsea tank to match that, rather than 24 hrs? Not sure if this would maintain levels better.

I previously have tried increasing the daily dose to try to account for the drop I saw even after setting up the initial dose. When I got to over 150 mL of dKH per day and I was still not able to get the dKH above 10, I gave up. It had to just be precipitating out because the Ca was dropping too. It got as low as 300.

Let me know if there are any other tests I can provide/use. Im getting sick of testing daily...
 

Randy Holmes-Farley

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10 dKH is fairly high in a new tank and may be driving abiotic precipitation of calcium carbonate.

Is the sand hardening? Pumps getting deposits?

This is my generic recommendation for precipitation issues (e.g., hardening sand):

1. Stop all efforts to boost pH.
2. Stop dosing alk for a bit and let it decline.
3. Reduce pH by switching to a low pH alk mix like sodium bicarbonate, or a calcium organic such as Tropic Marin All for Reef.
4. Ensure magnesium is normal to high.
5. Keep organics and phosphate on the high side.

After a few days of not dosing alk, restart slowly, adding additives to a very high flow area so it mixes in fast.
 
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Silverlava

Silverlava

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The sand is hardening! That makes sense then.

The alk mix I use is the 2 part from Bulk Reef Supply, which I believe is just sodium bicarbonate

I'll start dosing more organics. We've been light on the live phyto and frozen food we dose compared to our first tank.

How far should I let the alk drop before I try dosing again?
 

Randy Holmes-Farley

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The sand is hardening! That makes sense then.

The alk mix I use is the 2 part from Bulk Reef Supply, which I believe is just sodium bicarbonate

I'll start dosing more organics. We've been light on the live phyto and frozen food we dose compared to our first tank.

How far should I let the alk drop before I try dosing again?

It is probably sodium carbonate (soda ash) but they do also sell bicarbonate . Double check what it says you have.
 

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