The green water has nothing to do with sand being a bad substrate, it is fine. Your filter isn't moving much water, might want to add a powerhead to triple the flow to 10x tank volume per hour.
I remove debris that is on the surface and leave anything under there until the next big rescape which basically stirs up the whole substrate and it is rinsed a little. Dead plant leaves and fish poop get eaten by tiny critters and eventually turn into mulm which is the aquatic equivalent to compost. Good stuff in moderation and well in the substrate. When I moved from the 100 to the 180 gallon tank I didn't need to get the old tank outside fast as the smell from the layer of 10 year old mulm left in the tank was that of fresh clean earth, very nice.
4 bulbs? I am confused. Compact fluorescent bulbs are bent and come in 55 watt. T5HO are straight and come in 54 watt. Usually CF fixtures aren't as bright as T5 because of restrike and reflector quality. If you have 4 T5HO bulbs then you have too much light even if you are using CO2 which you didn't mention.
Cut back to 1 bulb if you can, 2 if you can raise the fixture up a bit or just put some window screen between light and tank no matter what kind of bulbs they are. That won't get rid of GW but it might keep it from coming back after it is gone. Two bulbs might be fine if these are CF, one might be better if these are T5s.
Or if you have floating plants let them build up until the GW is gone. Plants with leaves exposed to air are getting lots of CO2 and suppress GW. Takes a while and don't remove living floaters until the water is clear, not just better. Go through and remove old stuff though.
Vacuum the surface of the substrate during water changes but don't try to move any particles. I don't know if messing around with the substrate started your bout of GW but that is how mine always started in recent years. I was stirring up debris, a minute amount of ammonia was released and bam. Over and over again, it got real old. A year and a half ago I invested in huge sponges for my sump and haven't seen GW since even though I have been having a great time shifting things around in the tank, 2 complete tear downs and a move to another tank completely. I suspect stirring up the substrate a little combined with an inadequate biological filter=GW. You might try buying a prefilter sponge, the sort used on overflow box standpipes and putting it on your filter's intake to add a bit more biological and mechanical filtration.
Or have you tested nitrate? My first bout of GW was due to zero nitrate in the water. It is possible your bright tank has run out of nitrate and GW is taking advantage of the limited plant growth. Do you add any fertilizers to your tank?
Expensive but works, UV filter will slowly kill all the GW organisms. Or a diatom filter.
A black out sometimes worked for me and sometimes didn't. No plants died outright but I did have some seriously miffed stems. You don't want to see what Myriophyllum looks like after 4 days in the dark! Letting floaters build up worked much better for me than blackouts. If you want to try this be sure to cover the tank completely and no peeking. It takes more than a thin quilt to get the tank really blacked out. Feed the fish before the treatment and not during, be sure to have a good ripple on the water so it is well oxygenated and if you do have CO2 turn it off.
I answered a few days ago, but my post never showed up so I will try again. The tank is begining to clear up. I have had a comforter over it for 4 days now and will probably take it off tonight when I get home. I put a micron filter in an extra magnum 350 canister filter I had, but it got clogged up really quickly. I bleached it clean and am now letting it soak overnight in water + decholorinator so I can run it again tomorrow. Do I need to run this with diatemachious earth? I left it out the first time because I didn't want it to get clogged up too fast, even though it still only lasted a few hours tops.
Sorry for the confusion earlier, I will try to clear up some of the miscommunication:
1. Lighting: The lighting is 4 bulbs 54 (maybe 55?) watt compact flourescent. There are 4 pins arranged in a square at the end and the bulb is u-shaped. The light fixture is 48", with 2 separate ballasts controlling 2 bulbs (24") each.
2. CO2: I have a Ph controller/probe, CO2 regulator with solenoid, CO2 diffuser, and all of the tubing required to set up a CO2 system; the only thing I am missing is a CO2 tank. Is it worth the extra money to track down a tank, or would that money be better utilized somewhere else (tight budget).
3. Ferts: I have not started to add ferts to the tank yet. Originally, I was waiting a few weeks for the plants to settle into the new tank. Then the GW started and I am hesitant to add any more nutrition to the water in its current state haha. I have added root tabs next to the plants in the soil, but nothing that releases stuff into the water. Should I start adding this in now? I haven't tested nitrates but I will do that and get back to you.
4. Substrate: I am pretty confident that that is how the bout of GW started, and that is my main concern with the sand. If ammonia continues to build up approx. 1" below the substrate level, wouldnt any agitation (even accidental) become toxic to the fish extremely fast? If this is the case, wouldn't it be easier to maintain a tank with gravel (even though itd be a pain to switch at this stage)?
Also, does this still occur if the tank had only the aquarium plant substrate? The other half of the tank has a plant substrate (similar to fluorite or eco-complete) from aquariumplants.com. I am considering filling the entire tank with this, although not if it will cause complications similar to sand.
5. UV: I have an inline UV filter but the bulb is dead. Are these bulbs easy to replace? Once again, is this worth it or would the money be better allocated somewhere else?
6. Floating Plants: Are these essential for a planted tank? Right now, I have 7 Amazon Swords, although I will continue to plant their runners as they grow. I am also concerned that I do not have enough plants in there to adequately use up all of the nutrients, etc. If I remove the sand substrate and go with just the plant substrate, I would probably add some foreground plants as well.
7. New fish: Currently, there are two blue gouramis, a few snails, and a shrimp living in the tank. A buddy of mine wants to give me 4 gouramis and 5 tiger barbs from his tank (well established, 8+ months) this Friday. Should I hold off on acclimating new fish or will this be ok?
Essentially, I have a few bucks to throw into the tank but I am still on a really tight budget (college kid). I have unlimited time and energy though, so I prefer fixes that focus on these aspects, rather than financials
But seriously, thank you for your help. I've done a lot of research on all of the different aspects, but sometimes it is hard to simplify everything or synthesize it all together. I am planning on building a tank for my senior thesis so I am in this for the long haul! All/any advice is appreciated!