Hi
We set up a 70 litre tank 2 months ago using ADA Amazonia 2. We have used EI since the beginning using the recommended amount. Lighting at the beginning was 2x 24 watt T5s for 10 hours a day. We started getting lots of fluffy brown algae and got advice that we should reduce the lighting, crank up the CO2 (no fish in the tank) and double the EI dose. We did daily 50% water changes for the first week after set up and then 2-3 times a week for next 2 weeks.
We're still getting this fluffy brown algae plus some BGA and little plant growth. Any advice on how to flight this algae would be much appreciated. Thanks.

So you have a 20 some gallon tank lit by 48 watts of T5...

This seems like a lot to me. I would suggest reducing it either by removing a bulb or placing them further away from the tank top.

Go for a duration now of about 8 hours.

Here is a link on how to get a fresh start with algae:

Algae questions

When you got the earlier advice to lower the light, what did you do?

I see your duration says 10 hrs per day. Did you change this at all?

So, high light is an issue. Try reducing it and see.

Next co2.

How are you delivering this to the tank?

How do you know the concentration of c02 in the water? Are you using a drop checker with 4 d kh water to get a reasonable estimate?

You say you got advice to crank the c02. Did you?

What kind of filtration are you using? The tank needs to have good flow to get nutrients to the plants and to wash away waste products...

Please detail the amounts of macros and micros you are dosing and the schedule. You say you doubled, but what are you at now?

DO you still have no fish in there?

Do you have a lot of fast growing plants that will use the high light and nutrients you are giving the tank? If not, you are just feeding algae.

Plants need light, c02, nutrients to grow well. If they don't have these, they will not grow. The growth rate varies on the amount of these things the plants receive. Algae just needs less of these things to grow. Ammonia is also a big factor in algae growth.

If the tank has not cycled, you may still have high level of this.

Less light = less nutrient and c02 demand. Easier to manage.

Substrate - what are you using?

Hope this helps.

You ran out of nutrients!! You doubled the ei, but you did daily and then 3 times a week a 50% wc. I'm sure you are very low at nutrients.

Thanks for the reply - here are the answers to your questions.

Light - this is on for 8 hours a day and we have covered one of the tubes. We are using a luminaire.

CO2 - JBL pressurised with a ceramic diffuser placed under the filter intake. We have a drop checker using 4kh solution which is now kept very yellow.

Filter - Eheim 2324 which is rated at 700lph (10 x tank volume). We use two spray bars set along the back of the tank and the filter at it's maximum flow rate.

Nutrients - 1/4 tsp KNO3 3x per week; 1/16 tsp KH2PO4 3x per week; 1/2 tsp MgSO4 3 times per week; 1/16 tsp CSM +B 2 times per week. We then doubled the quantities or KNO3 and KH2PO4 about 2 weeks ago.

Fish - still no fish

Plants - we have added lots of H Polysperma and R Rotundifoila, there are also some crypts, Rotala green and some glosso (although this isn't doing too well).

Substrate - ADA Aquasoil Amazonia 2

During the first couple of weeks we tested ammonia and nitrite daily and saw the expected trends of a tank cycling.

I would increase all ferts but especially the nitrates (seeing as you have no fish in there anyway right now). H. polysperma can go through nutrients like crazy, especially with that amount of light and if you have a lot of it. When I had a big mass of that stuff in my 30g under LOW light, I had to add about 1/4 tsp PER DAY just to keep nitrates above 0. BGA thrives in high light/low nitrate conditions. Since I've been dosing nitrates I haven't had any bga issues at all. Prune all leaves that have algae (especially the H. polysperma, it will come back fast anyway). Clean out all algae that you possibly can, do a 50% water change/vac, then redose your nutrients and see what happens. Once algae takes hold, you really have to remove it before you can see if you are making any headway, it normally won't just die even when you fix the problem. I would test nitrates just out of curiosity. Yes, test kits aren't that accurate, but they will usually give you an idea if it's at or near 0 or not.