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When to change the 4dhk solution on the dropcheker?

I have seen a similar post m8 and the general census of opinion seemed to be when the colour fades because of the light to the point where you can't get a decent reading. The DC is itself a sealed unit so chemically speaking what you put in there at the start should be same as in there now as long as its not contaminated.
Most recommend 2 to 3 weeks.
 
I've always done mine once a week with the water change but on my last tank I noticed that one drop checker was getting much faster "results" than the other even when placed in the same place so I'm now curious of contamination as the theoretical difference is around 10ppm. I'd be interested in what you could use to clean the actual bulb, surely anything you add would leave a residue that would sway the "results", at the time I just used the 4dkh water but noticed no change in the reaction with one diffuser staying more bias...

Sorry for the hijack, just thinking outloud.
 
I used to wash mine out with 4dKH water like you but then it dawned on me one day while looking at both my jug that I mix stuff in for water changes and the sides of my electronic PH pen that sometimes there can clearly be seen a white powder residue left behind and wondered if this is also the case inside my DC possibly affecting the hardness of the indicator fluid. Now I rinse out my DC with de-ionised water 2/3 times and make sure every drop is out and dry before putting in the indicator solution.
 
I though DI water still had a residual hardness? My drop checkers were getting less hard, so maybe the opposite. Something I should look into when I set my tanks back up.
 
I though DI water still had a residual hardness?
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AFAIK DI and RO water should be totally devoid of any minerals theoretically being pure although I am new to all this so don't quote me on that :D Even the bottle I keep my 4dKH in has powder residue around the lid so even though I have not seen any on the DC I flush it with pure DI water hoping that if there is any it will dissolve into it and flush away.

The risk here being any left over will dilute the 4dkh although this is probably negligible and as it doesn't need to be dead on just void of any alkaline or acid bases I don't think it will affect the reading by much. I your case the 4dkh flushing if any was left over would be mixing with more 4dKH so shouldn't affect the result so is baffling.

I take it your using the same stuff in both DC's?
 
Hi,

I do mine monthly and thoroughly wash mine out in neat RO water then dry it with kitchen towel before refilling with the 4KH reference solution.

Regards, Chris.
 
Hi all,
All of R.O., Deionised & Distilled should be pure H2O, and totally devoid of everything. I would wash out in a weak acid (usually HCl, if their are any obvious deposits), and/or rinse in pure distilled and leave to air dry, because otherwise residues may build up. The white deposits are salts from evaporation. This is what we do with the glassware in the lab.
cheers Darrel
 
May be a stupid question but just checking HCl is Hydrochloric acid? when I look inside of my DC in good light I can see it's not totally smooth and the slight dimples often have a bit of colour residue in them. I have some aquarium plastic plant cleaner where the main ingredients are Hydrochloric acid just wondering if this will be safe to use and whether it will need diluted at all.
 
Hi all,
Yes HCl is hydrochloric acid, even when it is dilute it is still a dangerous substance, so you need to treat it with care.

Citric acid is another possibility, you can buy it from AVENT, they used it as the sterilising solution in steam sterilisers for babies bottle etc. Just found loads of it on "Citric Acid Descaler For Avent Sterilisers" EBAY <http://cgi.ebay.co.uk/20-x-10-Pkts-...vr_id=&cguid=fa3f2c3f1260a0aad4a4a3d4fed2250e> so that might be the best bet.

cheers Darrel
 
As a general principle, it's not a good idea to use acids to clean a dropchecker. That's because the dropchecker works by measuring acid content of the water sample. Any residues left over from acid application skews your sample pH reading, which can later result in false high CO2 readings, which then can results in Carbon deficiency if downward adjustments to the injection rate are made in response to the indicated colour.

Many dropcheckers have a narrow neck which prevents proper drainage of cleaning fluids so if you have discolouration or debris, it's better to use a small brush to clean it.

Cheers,
 
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