What caused this calcium deposit?

  • #1
DaveC426913
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Summary:
Plaque of calcium built up on my submersible glass aquarium heater Why here and why brown? And mostly, is there some electrical cause?
A have a deposit of calcium on the glass heater in my (freshwater) aquarium that does not seem to look or act like deposits I am used to.

To address some of the obvious questions:

A sample of it got nice and fizzy in a puddle of vinegar, so I have little doubt it is calcium.

I know calcium tends to build up on emerged surfaces in aquaria - especially reptile aquaria which require calcium supplements. This seems different.

It is not white; it is not powdery or delicate; it is not crumbly.
It is a medium grey-brown, very compact* and smooth** and hard enough that I risk breaking the glass trying to dislodge it with a knife.

*by compact I mean it is not spread out or patchy or uneven; it is a single, thick mass (1/8"), like a slug, in a very specific spot (next to one of the heater elements)
** by smooth I mean it has no fronds or fragile bits - it is like an old rock that has had all its rough bits worn off

The mass looks like this at least 1.25" long. No other deposits anywhere else on thermometer:
1618773911025.png


I found this thread that talks about calcium being "burned" onto the glass.

Questions:
  • Does calcium deposit differently in the presence of heat?
  • Is it possible the compact shape is derived from needing a "seed" to grow from, like a snowflake does (I forget what that's called in chemistry)
  • Why would this deposit grow so compactly? Is there some ionizing issue attracting it to deposit there, such as current leakage?



This is just a tiny sample. Piece on left has a glass-smooth inner surface
1618773557743.png
 

Answers and Replies

  • #2
BillTre
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Are there similar deposits elsewhere in the tank?
Brown stuff in freshwater aquaria is often "diatoms" (AKA brown algae), which usually have silica shells IIRC.
Here is a link to an article on them.
Calcium carbonate might become trapped among them as they grow.
The higher temperature of the heater may aid in its deposition.
What's going on in your aquarium WRT salts, pH, temperature, light levels, feeding levels, water changes, etc.?

I doubt it is electrical, unless the glass is cracked.

I might be helpful to consult with a local aquarium group. They might have dealt with similar water issues.
 
  • #3
DaveC426913
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Are there similar deposits elsewhere in the tank?
Brown stuff in freshwater aquaria is often "diatoms" (AKA brown algae), which usually have silica shells IIRC.
No, nowhere else.

This stuff is rock-hard - like coral. Needs to be broken off with a metal pick.

What's going on in your aquarium WRT salts, pH, temperature, light levels, feeding levels, water changes, etc.?
Tapwater pH around here is about 7.8. No salt. I only add water conditioner to neutralize the chlorine.

Turtles need a cuttlefish bone, just like parrots. It's no mystery where the calcium is coming from.

UV light and IR light on separate timers, about 10-12h per day.

I feed manually (turtle pellets). All food gets eaten. (Although turtles are notoriously messy when they poop.) I did a few rounds of feeder fish. Man they make a mess when they come out.

Powerhead with filter picks up any detritus pretty quick. Water has very good movement. I clean it every month.

I do a water top up every month (not actually a "water change". I'm so bad.). It's a 30gal tank, 2/3rds full, so maybe 20gal. I top up 2/3rds of that each month (evaporation). I really should be siphoning off some of the water, to remove buildup due to evaporation, but it doesn't seem to be a problem.

Water is clear. Not cloudy (i.e. no bacterial bloom). Little particulate matter. Minimal smell (which is saying a lot for a turtle)

No substrate, so it's not hard to keep clean and not hard to spot any buildup of detritus.

"Winston" has but a single companion: one (very fast) little feeder goldfish that she has not been able to catch.

I doubt it is electrical, unless the glass is cracked.
Yes, electricity is what is piquing my interest.

If the glass were cracked, I'd expect to find condensation and rust inside the glass heater from ingress.

I might be helpful to consult with a local aquarium group. They might have dealt with similar water issues.
Yes, I started with browsing for common terms. I find a lot about mineral buildup in the tank, but nothing about mineral buildup on the heater itself (or if they do, they tend to lean toward brown algae growth - which is not what I'm experiencing.)
 
  • #4
BillTre
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My best bet would still be on brown algae, encrusted in some way with the calcium carbonate, a favored by the high temperatures. Kind of like a stromatolite.

Your water probably has a high organic load. It also sounds like there is nothing else growing there, like plants (except perhaps in your filter) which would compete with the algae for stuff dissolved in the water.
I would do more water exchanges. Water has to be removed (not just evaporated) in order to remove dissolved chemicals. Most of the dissolved chemicals would have to physically removed (by water exchanges or by plants removing sucking up the chemicals, the plants could then be physically removed themselves.
Plants and more light for the plants could compete with the possible brown algae.

When I had turtle tanks as a kid, I would periodically remove all the water during a water change because it didn't hurt the turtles and was a very efficient water exchange.

Now I run an automated water exchange system on my (non-turtle) tanks, which once set-up requires zero (0) work and makes small water exchanges 4x/day.

Water chemistry combined with living things can get very complicated.
I once had some kind of bacteria growing in snotty fluff balls on pH electrodes. In some way, they were dependent on potassium leaking out of the electrodes.
 
  • #5
Lnewqban
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It is possible that the deposit has been forming on the hottest area of the glass, as the glass encloses a resistance that may not heat up the entire length of the glass tube due to modulation in order to keep a preset temperature.

I have seen apparently similar formations on the transfer surfaces of some steam boilers where water has not been properly treated.

Please, see:
http://www.sedifilt.com/technical_l..._part_i_why_water_treatment_is_necessary.html
 
  • #6
Borek
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A sample of it got nice and fizzy in a puddle of vinegar, so I have little doubt it is calcium.

No. Calcium is a shiny metal. Fizzing suggests it is a carbonate. Most likely calcium carbonate.

Brown/red colors often mean presence of iron, not that uncommon in tap water. Doesn't mean I reject diatoms explanation, I actually quite like it.
 
  • #7
Tom.G
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As I vaguely recall, the minerals in common tap water have lower solubility in hot water than in cold. That's why the hot water pipes, and heater, in your house clog up sooner than the cold water pipes.

That leads to the suspicion that there is a hotspot on the heater. Try replacing the heater (and the water!).

Cheers,
Tom
 
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  • #8
BillTre
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Hot spots in those kind of heaters are common.

My understanding of the greater clogginess of hot water pipes is the combination of a source of dissolved minerals (from the hot water heater and nearby pipes), combined with a lower solubility in the cooler peripheral plumbing (especially when the water is not flowing).
 
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  • #9
DaveC426913
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As I vaguely recall, the minerals in common tap water have lower solubility in hot water than in cold. That's why the hot water pipes, and heater, in your house clog up sooner than the cold water pipes.

That leads to the suspicion that there is a hotspot on the heater. Try replacing the heater (and the water!).
Thanks. Those two things combine to make a perfectly plausible explanation for my phenomenon.
 

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