Protein skimmer/biofilter query

Steve O'Shea

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This might sound bizarre, but do either protein skimmers or biofilters extract salt from the water? One of the tanks, in recirculation, with 2 x biofilter and 2 x protein skimmer, has a considerably lower salinity than another on flow-to-waste (that has 1 x biofilter and 1 x protein skimmer). I would have expected the recirc. system to have a higher salinity due to evaporation, and as I'm not experiencing any salt creep (to explain the lowered salinity), and am topping up with the same seawater running through the flow-to-waste system, I'm a tad confused.

The salinity drop is serious enough to kill squid if I were to remove them from the flow-to-waste system and place them in the recirc system (not that I've put this to the test; just a gut feeling). Sorry if a similar query has been posted earlier.

Can anyone shed any light on this wee problem?
Cheers
Steve
 

Colin

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In no particular order.. just as my brain thought it through! LOL

My first guess would have been salt creep. As long as you dont see that anywhere then i have no idea where it is going??? Not inside the skimmer or coating the fiter/filter media?

It is possible that a small amount of salt may make its way into the skimate but not enough to give you eroneous readings...

Are you using the same hydrometer/refractometer for both tanks???

The only other explanation is that for some reason the water going in has a lower salinity.. EG does the new water going in stay at a steady specific gravity or does it fluctuate? Is anybody topping up for evaporation too much?


Are the tanks at different temperatures????????????
This can give different readings and a true SG reading should always be taken at the same temp...

As an example for evaporation levels... an open top tank i had at 25deg C which measured 180cm by 75 by 75 lost approximatley 1 litre of water per day. This was mainly due to the skimmer and wet/dry biofilter... would not expect the opposite :bugout: :bugout: :bugout: :bugout: :?
 

Steve O'Shea

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Colin said:
Are the tanks at different temperatures????????????
This can give different readings and a true SG reading should always be taken at the same temp...
Bingo - the lower salinity tank is running at 17.5°C (has the eggs in it, lowered temp to delay hatching and produce larger hatching larvae), the higher at 22.5°C (to promote fast growth of the squid).

Ta muchly C; I'll check them at the same temp and see what it says then.
O
 

Colin

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Good stuff!

that's why you need me for looking after baby archies and messies etc :mrgreen: :mrgreen: :mrgreen: :mrgreen:
 

mikeconstable

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Condensation?

Most aquaria suffer evaporation because they are kept (or run) above the ambient temperature of the room. It sounds as if you are running a chilled system which might pull moisture from the atmosphere, do you have problems of condensation on the outside of the aquarium? Salt water contains deliquescent components and could absorb moisture even when no condensation was evident.
Interesting question for me is what temperatures are natural for your squid?, what will they tolerate? Will they only survive at lower temperatures as they get larger? (Limited by oxygen exchange surfaces increasing with the square of length, metabolism increasing with the cube of length?). Young fish tend to warm shallow water, larger fish to deeper cold water?
I have wondered whether skimmers could selectively deplete salt water of any trace components (but this would not affect salinity significantly)?
 

um...

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Re: Condensation?

mikeconstable said:
Interesting question for me is what temperatures are natural for your squid?, what will they tolerate? Will they only survive at lower temperatures as they get larger? (Limited by oxygen exchange surfaces increasing with the square of length, metabolism increasing with the cube of length?). Young fish tend to warm shallow water, larger fish to deeper cold water?
I've wondered that myself, but I keep forgetting to track down an answer. I was sort of assuming that gill surface area scaled fractally (i.e. between the square and cube of length), but I have no idea.
 

mikeconstable

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Length, area, volume relationships

The SIMPLE relationships are proportional to length, length squared, length cubed.
Exchanges occur across surfaces (areas), so oxygen, carbon dioxide (in gills), food absorbtion (in intestines) are limited by the square of length. The strength of tissue and muscles are also proportional to cross-sectional areas.
Metabolism occurs throughout the volume of the organism, so can be limited by the available rates of exchange. E.g. muscle power is proportional to area, but also increases in amplitude with length, so total output is a volume effect.
REAL relationships can have changes in structure (like fractals maintaining a minimum structure size as the whole picture expands). If there is a reserve unused (e.g. tissue strength might not be a limiting factor in gills, so the structure can become finer - there was an article in The New Scientist recently about carp growing modificated gill tissues in poorly oxygenated water) this can make life more complicated!
We usually find out the limits when the temperature of the aquarium shifts, or fermentation of old leaves at the bottom of the pond suddenly reduces oxygen below tolerable levels -- too late!
 

Steve O'Shea

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Re: Condensation?

mikeconstable said:
Most aquaria suffer evaporation because they are kept (or run) above the ambient temperature of the room. It sounds as if you are running a chilled system which might pull moisture from the atmosphere, do you have problems of condensation on the outside of the aquarium? Salt water contains deliquescent components and could absorb moisture even when no condensation was evident.
Massive condensation on the outside of the tank!!! My-oh-my, this is proving to be an interesting one. Thanks Mike.

OK; one more question. IS the salinity REALLY lower in the tank if it was just a SG/temperature related thing? Should I be adding salt to the tank, or doing more frequent and thorough water changes? Water is not the problem (squillions of gallons available), so it's no big deal.

Looks like I'll have to repeat the salinity test at the same temperature to determine how much surface condensation is actually going on.

Re the temp issue, I'll respond shortly; must go get more live feed.

Ta all.

O
 

mikeconstable

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Extra salt needed

Sounds like you are going to have to add extra salt in some way or other, but variations in temperature will make it either 'hit and miss' or rather slow.
Maybe you could reduce the condensation by having a cover over the tank but you will not prevent it completely if you have a skimmer or airstone?
Danger must be that the eggs will be damaged before you can notice?
Have any hatched in the low s.g. water yet?
 

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