SkylineView
New Member
- Joined
- Oct 30, 2022
- Messages
- 20
- Reaction score
- 10
- Location
- Houston
- What state or country do you live in
- Texas
Good afternoon fellow reefers. What follows below are my observations related to a white particulate in my substrate. I am not a reef tank of chemistry expert, but I do enjoy a mystery… and this is what I’ve latched on to today. I would appreciate your feedback or insights if you have come across this in your tanks or experience.
Summary of tank: 4.5 year old 75 gallon system (55 display, 20 sump). Substrate has been in the tank for approximately 3 years, and is a coarse black / purple material (I do not care for this substrate… but it’s what I have). The old substrate was a white sand, and it was fully removed to a clean bare bottom before adding the new substrate.
The levels and consistency of all tested parameters have changed dramatically in the last year; particularly for phosphate. The tank was fish-only and in poor condition a year ago, but today is a mixed reef with regular testing, dosing of primary elements (alk, calcium, magnesium, iodine, and trace elements), maintenance, and ~10% weekly water changes. Select parameters over time are below; ICP unless noted.
Jan 2026 (and for a period prior):
PH - 7.95
Phosphate (brace yourself) - 1.545 (this is ortho phosphate, reference range is 0.02 to 0.10)
Calcium - 478
Magnesium - 1416
Alk - 8.4
June 2026:
PH - 7.71
Phosphate - 0.11 (ortho phosphate)
Calcium - 417
Magnesium - 1319
Alk - 5.4
Early Aug 2026:
PH - 7.8
Phosphate - 0.13 (ortho phosphate)
Calcium - 395
Magnesium - 1314
Alk - 7.3
Current (my tests):
PH - 8.0
Phosphate (Hanna) - 0.08
Calcium - 400
Magnesium - 1350
Alk - 8.0
Observations: I periodically siphon portions of the sand bed to remove detritus. Upon doing so, there is a fine grained white particulate that appears in the siphon. This substance is not visible in the tank unless the substrate is disturbed; and after disturbing it, it disappears within 2-3 days. This material has appeared in the disturbed substrate for at least the past two years.
The material does not get removed via the siphon (I infer that it is too dense), but it does tumble in the siphon among the substrate and slightly above the substrate inside the siphon chamber. The particles are materially smaller than the substrate size.
Images below show the undisturbed substrate bed (with minimal white particles), and a section of disturbed substrate, in this case caused by a powerhead, exposing the particles.
Further observations: I removed approximately a tablespoon of substrate (roughly in the top half inch of the substrate bed) using a fine mesh net and placed it in a bowl of tank water. While the net easily captured the substrate, roughly 90% of the white particulate slipped out of the net due to the small particle size.
I used a (very cheap) microscope and a strong work light to look at the particles under several magnifications, and have included the images below.
To give some sense of the size of what we are looking at, here is a picture of the slide, with sample, and a usb-c adapter.
To my eye, these appear to be distinct granules or crystals of non-substrate material. They appear to clump, very loosely, to the substrate material and others of these granules. Clearly that connection is very weak, as they freely detach in the siphon, and when I netted the substrate material out of the tank.
Comparison to internet and AI identification: in researching this substance I came across many references to white string or “mold”-appearance substrate intrusions, but not the rock or crystalline structure that I see in the microscope. It also does not appear, to me, to be a sponge (another common response) or other creature.
Hypothesis: I have seen references to the rock and substrate of a reef tank acting as a sink for “phosphate”. I had inferred that this occurrence would not be readily visible to the naked eye, or if it was, that it would be a “powder” type consistency that would dust the rocks/return pump etc. I have not come across mention of a crystalline phosphate-related structure. That said, my phosphate levels were absurdly high for a long period of time; is it possible that I am seeing crystallized phosphate in some form?
Summary of tank: 4.5 year old 75 gallon system (55 display, 20 sump). Substrate has been in the tank for approximately 3 years, and is a coarse black / purple material (I do not care for this substrate… but it’s what I have). The old substrate was a white sand, and it was fully removed to a clean bare bottom before adding the new substrate.
The levels and consistency of all tested parameters have changed dramatically in the last year; particularly for phosphate. The tank was fish-only and in poor condition a year ago, but today is a mixed reef with regular testing, dosing of primary elements (alk, calcium, magnesium, iodine, and trace elements), maintenance, and ~10% weekly water changes. Select parameters over time are below; ICP unless noted.
Jan 2026 (and for a period prior):
PH - 7.95
Phosphate (brace yourself) - 1.545 (this is ortho phosphate, reference range is 0.02 to 0.10)
Calcium - 478
Magnesium - 1416
Alk - 8.4
June 2026:
PH - 7.71
Phosphate - 0.11 (ortho phosphate)
Calcium - 417
Magnesium - 1319
Alk - 5.4
Early Aug 2026:
PH - 7.8
Phosphate - 0.13 (ortho phosphate)
Calcium - 395
Magnesium - 1314
Alk - 7.3
Current (my tests):
PH - 8.0
Phosphate (Hanna) - 0.08
Calcium - 400
Magnesium - 1350
Alk - 8.0
Observations: I periodically siphon portions of the sand bed to remove detritus. Upon doing so, there is a fine grained white particulate that appears in the siphon. This substance is not visible in the tank unless the substrate is disturbed; and after disturbing it, it disappears within 2-3 days. This material has appeared in the disturbed substrate for at least the past two years.
The material does not get removed via the siphon (I infer that it is too dense), but it does tumble in the siphon among the substrate and slightly above the substrate inside the siphon chamber. The particles are materially smaller than the substrate size.
Images below show the undisturbed substrate bed (with minimal white particles), and a section of disturbed substrate, in this case caused by a powerhead, exposing the particles.
Further observations: I removed approximately a tablespoon of substrate (roughly in the top half inch of the substrate bed) using a fine mesh net and placed it in a bowl of tank water. While the net easily captured the substrate, roughly 90% of the white particulate slipped out of the net due to the small particle size.
I used a (very cheap) microscope and a strong work light to look at the particles under several magnifications, and have included the images below.
To give some sense of the size of what we are looking at, here is a picture of the slide, with sample, and a usb-c adapter.
To my eye, these appear to be distinct granules or crystals of non-substrate material. They appear to clump, very loosely, to the substrate material and others of these granules. Clearly that connection is very weak, as they freely detach in the siphon, and when I netted the substrate material out of the tank.
Comparison to internet and AI identification: in researching this substance I came across many references to white string or “mold”-appearance substrate intrusions, but not the rock or crystalline structure that I see in the microscope. It also does not appear, to me, to be a sponge (another common response) or other creature.
Hypothesis: I have seen references to the rock and substrate of a reef tank acting as a sink for “phosphate”. I had inferred that this occurrence would not be readily visible to the naked eye, or if it was, that it would be a “powder” type consistency that would dust the rocks/return pump etc. I have not come across mention of a crystalline phosphate-related structure. That said, my phosphate levels were absurdly high for a long period of time; is it possible that I am seeing crystallized phosphate in some form?
