[Dewi_Sant]

Hi - Please bear with me whilst I try and explain my question - I have added as much other possibly relevant info as I can:-
Other than the general tests I carry out on the water of my tropical saltwater marine aquarium - PH - Nitrate, Nitrite, Phosphate, calcium, and hardness etc I am a complete novice as regards chemistry - I started  with a 4 foot x 2 foot tank but the fish have outgrown this tank  so I have just installed a 9 foot x 3 foot one - when using the 4 foot tank 2 x 10 gallon containers was plenty for the regular water changes required - My R.O. unit can only process 50 gallon a day maximum - now as this tank plus the sump require 500 gallons to fill I needed a far bigger storage tank for the RO water so I purchased a 1,000 litre plastic container that was from a cheese factory - it had contained a food colouring called Annatto (E160B) Extract - Double strength - there is plenty of information on it through Google if you are chemically conversant but 2 a thicko like me it looks like a minefield - now there is a warning label on the container that states *Irritating to eyes and skin - contains Potassium Hydroxide* now with what do I need to wash this tank out with that would destroy any residue of the colouring extract - once it fills with the RO water I will be adding saltwater crystals to a SG of 1.026 and another chemical 'Propper PH 8.4'  and it will be heated to 25 deg C - any of which could possibly cause a reaction  to any annatto residue left or to the marine fish and crustacions

Any help/advice would be much appreciated - Dewi

[harnessk]

The residue in the  container is most likely not that concentrated or you would have never been given it.  I would start by giving it a good blast with a garden hose or shower to remove most of whatever is in there.  The problem lies with the annatto.  It is oil soluble in most cases, and coming form a cheese factory I could almost guarantee this is the case.  So, you're going to have to get hold of a good soapy cleaner and scrub it really well.  Then go back to the garden hose and get rid of the soap.  Keep doing this until you're satisfied that it's clean.

[Dewi_Sant]

Harnessk
Thanks for the reply - as the tank has only a 4 inch cap on it it is difficult to scrub out - I have hosed it out but with the water shortage at present I feel awkward about wasting it - we at present have no restrictions but I have already filled it to overflowing once then let it out -

Is there no way I can tell if it is actually free of the stuff - what is potassium hydroxide and how many ppm would be dangerous to the livestock?

Are there any other 'nasties' I need to be careful of in there?

Could I for instance scrub it out and then rinse it out - then send a sample off somewhere for testing?
Thanks in anticipation of your help
Dewi