Is this 2-part dosing correct or am I missing a larger issue?

[Tides]

60 gallon cube, 20g sump
Tank age - 2 years
Moderate sps/lps/softies (about 29 frags) and an 8" derasa clam (takes up most of the sandbed...)
15% water changes weekly - Fritz RPM - Sg 36ppt
Deep sand bed, live rock
Radion XR30wpro g4 w/diffuser AB+ at 90% for 10 hours, 11" up.
Octo130 internal skimmer
77.5 degrees Farenheit
Alk - 8.7-9 (low end towards the end of the week)
Ca - 380-410 (low-end towards the end of the week)
Mag - ~1420

Currently dosing BRS 2 part every 1 hour at 30 minute intervals between soda ash and calcium carbonate over a 24 hour period. Dosing tubes fall into sump into a mini powerhead aimed at return pump.
I currently have my dosing set to...
Soda ash solution - 110ml/Day
Calcium carbonate solution - 135ml/Day

I do not manually adjust during the week and I check my levels every two days. After water changes my levels are great, but I always notice a slow decline in primarily my calcium then kH levels while Mag tends to stay level.

What am I missing here? Something seems off when comparing to others with much larger volumes and more heavily stocked tanks...

 

[chipmunkofdoom2]

Dosing tubes fall into sump into a mini powerhead aimed at return pump.

Do you mean to say that the dosing tubes actually make contact with the water? If so, this could be part of your problem. Dosing lines should never be submerged. Seawater mixing with the highly-concentrated solutions in the tube could be causing local precipitation, which would prevent the additive from ever increasing calcium and alkalinity, respectively.

About the consumption rates. From your dose it looks like your tank is using about 2 dKh/day (more if the levels drop over the week). If you have 29 frags as well as a clam that takes up the entire sand bed, this doesn't sound unreasonable when you factor in some abiotic precipitation. Which could be happening in your DSB. Are the frags growing at a steady rate?

 

[Tides]

Thanks for the quick reply, first and foremost.

The tubing is about 1" off the sump water surface, so not submerged. It is about 1" away from the sump wall as well so it is dripping into the water. So far, based on readings from this week, I will be increasing my dosing further.

I do have explosive growth on things like my montis and certain millis, but my lps either struggle or grow slowly (IE my orange crush echinata is browning, but my acans are showing great growth). Platys and chalices show slow-moderate growth. Coralline growth is steady, but mostly inhabiting the glass/piping before getting to the rock. Some sps like my oregon tort have been building a steady base at a few mm/a cm or so each month.

Excuse my ignorance, but what do you mean by "DSB"?

 

[Randy Holmes-Farley Verified Community Expert]

I assume you mean the calcium additive is calcium chloride. Calcium carbonate is not suitable.

If calcium is declining, and alk is steady, just add more of just the calcium part. Your pumps may not be matched, water changes can mess with the demand ratio, and some other minor effects can account for the differences you observe.

 

[Tides]

I assume you mean the calcium additive is calcium chloride. Calcium carbonate is not suitable.

If calcium is declining, and alk is steady, just add more of just the calcium part. Your pumps may not be matched, water changes can mess with the demand ratio, and some other minor effects can account for the differences you observe.

Yes, you are correct, calcium chloride. Can you elaborate on the pump matching?

 

[Randy Holmes-Farley Verified Community Expert]

Yes, you are correct, calcium chloride. Can you elaborate on the pump matching?

Many dosing pumps do not deliver exactly what they are rated to deliver in mL per min or mL per hour.. Unless you do a 24 h measurement of the pumped fluid, you may find that you cannot simply multiply the time by the claimed rate to get the actual dose. That's one reason some folks have found a need to dose "unequal" parts, and maybe you actually are dosing closer to 1:1.

 

[madweazl]

That seems like a pretty high consumption rate for frags and other corals that use little to begin with. Are you using something like BRS (Randy's recipes) for the 2 part? I'm using about 33ml/day with a couple smaller colonies (6-8") and 15 or so acropora frags; this certainly doesnt mean yours arent growing faster than mine but if they're frags that are just encrusting at a rate of a couple millimeters/month, they're using next to nothing.

 

[Tides]

That seems like a pretty high consumption rate for frags and other corals that use little to begin with. Are you using something like BRS (Randy's recipes) for the 2 part? I'm using about 33ml/day with a couple smaller colonies (6-8") and 15 or so acropora frags; this certainly doesnt mean yours arent growing faster than mine but if they're frags that are just encrusting at a rate of a couple millimeters/month, they're using next to nothing.

Yes, they are all for the most part still forming their bases. I only have one large colony of echinata, maze brain, and the derasa. I'm still not sure where I need to have my light levels, so who knows. Every system is different.
I am using the BRS directed solution, found on their website/given instructions for dilution in their 1 gallon jugs.
The suggested Soda ash dose with their solution to raise 80 gallons of water 1.4 dKh is 80mls. So with that math, my system is using more than 2dKh/day (114mls).

 

[madweazl]

I understand what you're dosing and why but are you actually consuming 2 dKh per/day or is a substantial amount of it precipitating?

 

[Tides]

I understand what you're dosing and why but are you actually consuming 2 dKh per/day or is a substantial amount of it precipitating?

I misunderstood your question, so I apologize for the unnecessary explanation. That is certainly the question at hand! With interval dosing on a monthly calibrated pump spread out every hour of the day, how could I be losing that much to precipitation?

 

[Randy Holmes-Farley Verified Community Expert]

Some soft coral tanks can consume 2 dKh per day. Coralline uses a lot, for example, and some amount precipitates in every tank (unseen, typically, except on pumps and heaters). A big clam also uses a lot.

 

[Tides]

Some soft coral tanks can consume 2 dKh per day. Coralline uses a lot, for example, and some amount precipitates in every tank (unseen, typically, except on pumps and heaters). A big clam also uses a lot.

Ok then! I'll keep adding until I stabilize over a week. What is the recommended increase usually? I have just been doing rough calculations on the difference based on where I start after a WC and where I end up at the end of the week.

 

[Randy Holmes-Farley Verified Community Expert]

Ok then! I'll keep adding until I stabilize over a week. What is the recommended increase usually? I have just been doing rough calculations on the difference based on where I start after a WC and where I end up at the end of the week.

That's a fine way to do it. Alk demand ranges from almost none to over 4 dKH per day in some heavy SPS tanks.

 

[Tides]

That's a fine way to do it. Alk demand ranges from almost none to over 4 dKH per day in some heavy SPS tanks.

Thank you for the help!
I spent some time and actually measured the actual volume in my sump and it was ~12 gallons, so assuming 60-gallon tank with about 15 gallons of rock, the total volume of water should be around 57 gallons. Readings from last night 5 days into my last water change was..

KH: 8.7
Ca: 410
Dosing 110mls Soda Ash solution/Day (increased to 120ml)
Dosing 135mls Calcium Chloride/Day

So it seems that my calcium is finally slowly building instead of getting used up...
But now my question is, how is the equilibrium between KH, Ca, and Mag related? Does consumption of Ca depend on KH levels and the buffering Mag? I would be more than glad to read a scientific article explaining this if anyone has quick access to a link or an amazon book I can pick up

 

[Randy Holmes-Farley Verified Community Expert]

Thank you for the help!
I spent some time and actually measured the actual volume in my sump and it was ~12 gallons, so assuming 60-gallon tank with about 15 gallons of rock, the total volume of water should be around 57 gallons. Readings from last night 5 days into my last water change was..


So it seems that my calcium is finally slowly building instead of getting used up...
But now my question is, how is the equilibrium between KH, Ca, and Mag related? Does consumption of Ca depend on KH levels and the buffering Mag? I would be more than glad to read a scientific article explaining this if anyone has quick access to a link or an amazon book I can pick up

For coral calcification (skeletal growth) or abiotic (nonbiological) precipitation, the relative amounts used are about 2.8 dKH (1 meq/L) alkalinity, 18-20 ppm calcium, and ~0-1 ppm magnesium.

When alk and pH are higher, demand (use) rises, both by corals and by abiotic precipitation.

Calcium has little effect on either, unless it is super low or high.

Magnesium can have a small effect on abiotic precipitation, increasing it when mag is low and decreasing it when mag is high.

 

[hart24601]

That big clam will use a whole lot of 2 part. Think about how much that shell weighs, then remember that not only does the shell grow outward, but also gets significantly thicker. All that new shell comes from 2 part and even at 8" it can still be growing fast!

 

[Tides]

Very true - I now know derasas are absolute resource hogs.

I totally forgot to add my pH into my parameters.... it is 8.4.

So I can keep my calcium fairly high (~440) with minimal effects to (metabolism?) demand, as KH is going to regulate metabolism/demand rate. I just need to match my calcium dosing to the demand.

Magnesium is the buffer for abiotic precipitation, so I want that as high as possible (~1800?) to increase solubility factors of my 2 part?

Please teach a marine biology course I can take, Dr. Farley.

 

[Randy Holmes-Farley Verified Community Expert]

Very true - I now know derasas are absolute resource hogs.

I totally forgot to add my pH into my parameters.... it is 8.4.

So I can keep my calcium fairly high (~440) with minimal effects to (metabolism?) demand, as KH is going to regulate metabolism/demand rate. I just need to match my calcium dosing to the demand.

Magnesium is the buffer for abiotic precipitation, so I want that as high as possible (~1800?) to increase solubility factors of my 2 part?

Please teach a marine biology course I can take, Dr. Farley.

Calcium concentration seems to have little influence on corals in the 400-550 ppm range.

No, you do not want magnesium as high as possible, and minimizing abiotic precipitation is not typically a goal of most folks unless they have a specific precipitation event ongoing. If they do, there are specific plans of attack that, IMO do not optimally include excessive magnesium. They include stopping alk dosing for a while, lowering pH, and allowing organics and magnesium to coat fresh calcium carbonate surfaces that are acting as seed crystals, then resuming dosing normally.

This link (stickied at this page top) lists lots of articles that detail all the chemistry you are likely to want

Randy's Reef Chemistry Articles
https://www.reef2reef.com/threads/randys-reef-chemistry-articles.174821/

 

[Tides]

So I've done a good bit of reading (thank you Dr. Farley) and chatted with a few people... it seems like I may be missing something still.
BRS states that 0.3ml/gal of 2 part is a baseline for heavily stocked tanks. This means about 21ml/day.
I'm currently up to dosing 190ml/day (3.2ml/gal) of 2 part and my kH will not go over 8.7 and my calcium will not break 410. It is like no matter how much I increase it I can only stay at 8.7kH and 390-400 calcium.
I have tried testing with different kits and get similar results. Magnesium stays about the same and I typically don't even dose that. I've calibrated the pumps and verified the amount they are dosing. Checked to make sure the tubes are not submerged and being dropped directly above the return pump. Have been staying on a strict 10% W.C. schedule weekly.

What am I missing here? Shouldn't my kH and Calcium levels be sky-high given the BRS values?