Protein skimmer/biofilter query

[Steve O'Shea]

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]

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 :?

 

[Steve O'Shea]

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]

Good stuff!

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

 

[Steve O'Shea]

 

[mikeconstable]

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...]

Re: Condensation?

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]

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]

Re: 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.

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]

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?

 

[Steve O'Shea]

Re: 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?

About 50 eggs have hatched so far, and the squid appear fine (although they're not in there for any longer than a couple of hours); they're moved immediately to another tank (first thing in the morn; they tend to hatch only in the morn). There are about a thousand larvae ready to hatch from these eggs.

I'm not happy with the colour of the water either (it's a bit dark), and I might be verging on neurotic, but it also feels grainy (it just doesn't feel right), so I'm giving it repeated draining (1/3rd at a time) daily. There are 2 protein skimmers and 2 biofilters (new carbon) working away on that tank now; the protein skimmers aren't taking a lot out right now, though a couple of days back they were extracting quite a bit). I just don't like things happening in tanks that I don't understand. Probably have a few too many things on right now, and quite a few things are slipping.

I cannot drain the entire tank as any disruption to the eggs will cause premature hatching and pretty much loss of all larvae.

 

[Colin]

You never actually mentioned what the SG is in the two tanks, i dont think i would do anything to change the salinity, you have such a bonus in having it on tap, it would be a shame to have to mess about with salt.

A brand new skimmer can take a couple of weeks to work properly, always seem to do better once they get a film of scum/bacteria inside the column. If they are not removing anything it normally means that there is nothing to remove.. sounds too easy but a 1/3 a day water change is more than enough to remove toxins.

No idea about the dark water but different manufacturers of tanks use different glass with different tints, also some glass like 'K' glass can feel grainy so it may just be that???

Why move the newly hatched? How do you do it and is the tank you move them to at the sam etemp SG etc????

Dont worry, this'll work this time

 

[Steve O'Shea]

A brand new skimmer can take a couple of weeks to work properly, always seem to do better once they get a film of scum/bacteria inside the column.

Why move the newly hatched? How do you do it and is the tank you move them to at the sam etemp SG etc????

Dont worry, this'll work this time

Howdo C; I'll repeat the SG measurements morrow and fire 'em through. Strangest thing. I'm in a room that might reach 25°C at this time of year, and the chilled tank is running at ~ 18°C. The condensation on the outside of the tank is significant. So I mentioned Mike's post about the condensation IN the tank (at the air/water interface) and the curator there says ..... and I'm scared to repeat this .... not an issue. I can see where he is coming from. I'll be experiencing evaporation (because of the temperature difference, but I'll also be experiencing condensation ... and that the two 'just might' compensate. Mike??? Difficult isn't it; 6 of this and half a dozen of the other?

Bizarre. I do have special lids for these tanks, but not a lid that will allow the protein skimmer to fit (they're rather ungainly things aren't they; there must be a model that you don't have to have inside the tank .... I'll do a search when next at the pet shop ... or, as you say.... LFS [learning the lingo]).

... now, C, you have me scratching my head. These squid are on public display, and a dirty film on the protein skimmer just doesn't look good. So, in addition to cleaning them out daily (or every second day), I get rid of that scum lining the funnel. Am I doing wrong?? They're obviously working, but I'm inclined to believe you for 2 reasons: 1) you know what you're talking about, and 2), I think the amount of crap that deposits in the container increases with the amount of scum deposited on the funnel. You know, this is a rather easy experiment to see whether this is true or not - just have several identical protein skimmers in one tank, clean one regularly and just empty the container on the other (same periodicity). Let's do it!
Cheers
O

 

[Colin]

ok game on!!!!!!

i do think that they need cleaned from time to time but some of my best skimmers have ran literally for months and got better with age the collection cup itself (not the main tube) should be cleaned on a more regular basis proportional to scum collected.

if you really really really wanted to get into it there is an entire science about foam fractionators... its all to do with stuff like bubble size.. length of time in solution.. bacteria at work in riser column etc etc... if its pulling out crap its working that works for me. but please try the experiment... im interested...

hows abouts drilling the tanks and using sumps therefore the equipment can all be hidden from public view????

i would be tempted to have a big sump... 100gal+ with a constant drip drip drip of new seawater... slow enough to not affect temp but big enough to do a constant water change... might not even need skimmers then? you could supply as many tanks as need be from one sump

 

[mikeconstable]

Condensation!

Colin is right when he suggests you could bleed in new salt water and run the excess old water to waste. I would have thought that if the sg had decreased very significantly you might have noticed the increase in volume? (unless the excess just flowed to waste?)
If the water temperature is below the dew-point of the air there will be no evaporation, only condensation - a one-way flow.