I'm not 100% on what it is, but I belive it feeds of silicates from new silicone while it is still settling down. I have had something similar in all the new tanks I've set-up over the years, but none in any second-hand tanks... My fish ate it when they were introduced on all occasions, so it's probibly plant life of some sort, I wouldn't worry about it
While you fishless cycle, you may want to crank the temperature up to about 30c untill you are ready for fish, when you can drop it to about 26-27
The increased heat will speed the maturation, and since there won't be any fish in there while that is going on, it won't be too high for fish
Lets just check what you have;
Liquid-regent based test kit for ammonia, nitrite, nitrate and pH?
Liquid ammonia?
The stingray filters use zeolite, so I'd remove this filter cartridge, and swap it with the mature media you get later
I work in an LFS, so this is where I'd prefur to take mature media for collection, if you are taking any from me? I can sort you out with test kits when you collect the media if you need them, but ammonia isn't something LFS's stock, so this will need to be bought from a chemist before you collect the media
I use Boots household
Drop me a PM for details if you want media.
Zeolite absorbs ammonia. Thats a good thing isn't it? Well, no as it turns out
Zeolite eventually becomes saturated and then is stops doing it's job... If this happens there will be an ammonia spike in the tank, which almost certainly will lead to deaths. You can bet that this will hapen when you have forgoten to collect the new replacement cartridge and don't have any spares in stock, so you'd have to rush to the nearest LFS for new media to remady the situation. The cost of zeolite IMO is also extortionate, and there are cheaper and IMO better ways of running a tank; on bacteria. Zeolite also cannot be used with meds, so if you needed to treat anything, you would have water quality issues when you least want them
Best to get it out from the start, and avoid the situation entirely
Because zeolite absorbs ammonia, it out-competes the bacteria for it, sending the biological filter up the creak without a paddel to help it.... not good
Swapping the zeolite out for mature media will avoid this issue and give you a tank that runs on mature filter media and bacteria that stay when treated with any medication, and that don't become saturated, thus giveing more reliable ammonia removal
Does you dad keep fish then? If not, and you want to get him to care for them while you go on holiday, I'd get him on here to learn about the nitrogen cycle, water testing and the most common diseases that he may come across in your abscence. Also, him signing up with a user account on here and letting us know whom he is, would allow us to help him if something goes wrong and he becomes out of his deapth and in need of help
If we know whom he is, and that he is careing for your set-up (one we already know a lot about) then we will be in a better position to help, if you cannot help him diagnose the problem over the 'phone
All the best
Rabbut