i would defiantly go separate, and i would highly recommend a glass drop checker too, i have a plastic one and it has leaved on the odd occasion, i would also recomend buying one from AE more expensive than Ebay but at least you will get yours i bought 3 with a bubble counter and i am still w8ing on them been 2 months now and the seller has send me another batch which again still not got here,
http
/www.aquaessentials.co.uk/neutro-drop-checker-p-1231.html
you will also need this
http
/www.aquaessentials.co.uk/neutro-bromo-blue-250ml-p-5487.html
i got the latter one as its already pre mixed you can do it your self if you wish but i didn't want to.
thats the only two things you need altho i would recommend getting a pipet as it makes it a little easier to get the right amount of fluid into the drop checker
just to note the plastic one i got was this
http
/www.aquaessentials.co.uk/colombo-floragrow-co2-indicator-p-5022.html
it dose work but every now and then it will leak
oh and i forgot that 250ml solution dosnt seem allot but you generaly use about 3ml every 1 week to 3 weeks so it will last you years