You could try
GLA but they are a US company. I don't know what is available in the UK.
Note after some recent findings on another aquarium site GLA modified the micro mix by adding additional zinc and iron DTPA. The iron DTPA works better at PH above 6.5. CSM uses iron ETA which doesn't work above a PH of 6.5 while DTPA will work up to a PH of 7.5 and maybe up to 8. and and CSM was found to be deficient in zinc.. With the change you might only need to dose micros once of week.I make my own macros and I only dose once a week and target a iron dose of 0.1 Fe. It is really quite hard for plants to consume more than 0.1ppm of Fe a week. Many others are still selling the CSM+B recipe which only has iron EDTA and is deficient in zinc.
As to macros you can also get by with a once a week dose. The key is to make sure you have all nutrients covered by your fertilizer. The original EI recipe only specified NPK dosing. It ignored the other 4 macros calcium, magnesium, sulfur, and chlorine.(Yes plants need some Chlorine but not as a toxic gas but as a chloride salt). A lot of people have run into Ca, Mg, S problems.
Tap water does typically have Ca, Mg, S, and CLbut it occasional doesn't or in my case I was using RO water whichdefinitly doesn't have these. I typically target 10ppm no3, 1ppm PO4, 12ppm Ca, 4ppm Mg, One dose a week is all I need for my macros. I don't have a target for potassium (K) since 10ppm NO3 with KNO3 supplies more than enough K for plants. I also not have a target for S and CL since I am urgings calcium sulfate and magnesium chloride. which with the Ca and Mg targets I have listed also supplies S and CL at above what plants need. I also don't use potassium sulfate which is often recommended for EI. My excess Cl and S does cause n water PH to slowly drop in my RO water tank. I resolve that dope by putting a decorative sea shell in the tank. it neutralized the excess Cl and S and keeps my PH very close to 7.
As to CO2 I use the
inverted bottle methode to dissolve it in my water. This insures all the CO2 your by dissolved in the water with bubbles or defusers you always have some bubbles that don't dissolve and rise to the surface. In my 5 gallon tank my 21 once bottle lasted about 3 months with a defuser. Now with the inverted bottle methode it last about 1 year. Note drop checkers don't work with the inverted bottle method and yet I don't see anything to indicate I am low on CO2. With the inverted bottle CO2 method you cannot kill your fish with too much CO2. Also not PH cannot be used to measure CO2 levels. Many minerals and salts in the water will have a much stronger affect on PH than CO2 does.
As to lighting check your water PH once in the morning before lights turn on and once just before the lights turn off. Most would expect the PH to stay constant but I found it doesn't. In my tank it tends to slowly rise with the lights on If it gets above 7.5 you will start to loose iron. The solution to this issue is to then dim the lights As plants consume nutrients the PH will change since water chemistry is changing.
I hope this advice will help you once you get your fertilizers.
