My 28G Fish Tank - Opinions?

Hi I wanted some opinions on my 28 gallon.  I have a few questions too.  Here's what I have in it:
 
1 Bullfrog Tadpole
1 Angelfish
1 female betta
1 Siamese Algae Eater
1 Rosy Red Minnow
1 Nerite Snail
1 Ghost Shrimp
 
I have a little bit of everything it seems.  It's moderately planted, and I'm always looking to add in more plants and will continue to do so (it's an obsession!) .  I love the plants, they're beautiful and easy to grow.  I keep the tank by a somewhat open window, which allows some lovely light in but unfortunately allows a little algae growth as well.  Right now the nerite snail and the siamese algae eater are doing a great job on the algae, but there's still more algae to be cleaned because I allowed a little more light in the window recently, and the plants love it but so does a few tiny spots of algae.  I was thinking about adding a few more nerite snails to the aquarium, eventually bringing up my snail count to somewhere between 4-6.  Is this okay?

I was also thinking about adding another angelfish, I heard they are bad to be kept solo.  Do you guys think that this is okay to do?  Or is the tank too small?  Would the bioload be too high... What is the bioload looking like right now, in your opinion?
 
Hopefully the plants clean a lot of the bioload up .  I have hornwort, and wysteria, a few anacharis, and tons of other plants I have no idea what they're all named
 
I'll also post a picture.

Here's a photo of my tank!  It's a bit small to see, sorry, but you can actually barely see the angelfish to the left of the castle - he's camouflaged very well .

It would help if you could answer these questions;

what are the dimensions of the tank?

is your water hard or soft?

what level nitrate do you have, in your tap water, and in the tank before a water change?

The dimensions of the tank are around 30 inches across, 18 inches tall, and 12 inches back. 
 
The water that I use is hard
 
and I'm not sure about the nitrates.  I haven't measured that, I am only measuring amonia right now.  I've had a pet store check the other paramaters and everything is okay except for the water ph, which she said was a little high, around 7.4 or something.  However, she said that the water in this area its PH was usually a little high like that.

Might be worth getting your own liquid water tests as you can quickly check something if something goes amiss and easily prevent things from going amiss in the first place by being proactive rather than reactive. Basic tests are available in master-kits such as API and generally work out cheaper than buying individual ones. 
Also LFS' tend to say things are OK and not what the readings are. Personally, without knowing what the numbers are, I wouldn't be happy with "OK".
When adding your new snails, be aware that they can produce quite a lot of waste and possibly more than the beneficial bacteria in your tank can cope with, causing a mini-cycle where ammonia builds up because it can't be processed quickly enough. Not trying to put you off - just point out a possible outcome.

I wouldn't add another angel. Being cichlids, they like to choose their own mates and the chances of two random angels being friends is quite small. If you wanted a pair, you'd have to start off with about six young ones and wait until a pair formed, then rehome the rest. Angels actually do fine as solo fish.

You do need more minnows, as they are a shoaling fish that really do need company of their own kind to be happy.

I also agree with Mamashack; you should definitely get some test kits of your own, before you think about getting any more fish.

I agree on the angelfish.  One should ideally have a small group, five up, but that means a 4-foot tank like a 55g or larger.  A bonded/mated pair can work in a 29g, as one would have for spawning (removing other fish obviously), but with the present situation I would leave things alone.  I personally do not like to see angelfish alone, or in anything less than five, but having said that I accept that some aquarists do have a single angelfish that seems to be fine.
 
I also agree with others on the test kits; the API Master Combo (liquid, not strips) would work for you.  Online it will likely be less expensive.
 
By the way, when hard/soft was previously mentioned, the reference was to the GH or general hardness.  The pH is related, but the GH is actually more significant for fish assuming the pH is not way off the fish's preference.  Rather than buying another test kit you may never use but the once, check with your local water supply people, on their website, or contact them.
 
You are aware I hope that the Siamese Algae Eater will attain six inches?  You might want to consider re-homing this fish.  It too is a shoaling species, meaning they should be in a group, but here again many keep individual fish though I wouldn't.  But given its size, it will be "obvious" in a 29g tank.  Also, there are other so-called "algae eaters" sometimes sold under this name but they are different species, and some have rather nasty dispositions as they age, while most eat algae less and less.
 
Byron.

Thanks for your replies everyone!   

Yes I would like to leave this angelfish as a solo fish for now, as long as he will be happy.  He's not small but he's not full-sized either, he's about medium sized, so he still has some time to grow.  I'm glad that they do decent as a solo fish.  Another option too is that my local fish store said they'd be happy to buy him back once he reaches full size if he's too big for my tank or doesn't get along, but I got him because my girl wanted an angelfish and so far he is doing wonderfully.  He seems to be super curious and interested in me and he loves to watch me and I love to watch him.
 
I've also added another minnow and will add another 1 or 2 as time goes on, I know they are schooling fish.  I originally had more than one, but several of them died because they were in poor health when I got them :\
 
I did add some more snails as well, I wanted them eat the algae up so I could let more light in the tank.  I'll monitor the amonia, and I'll monitor the other levels such as nitrates and nitrites as well.   
 
And I added some beautiful new plants, of course!
 
Thankyou for your help everyone.

Actually that angel is still quite small, from what I can tell. You will be surprised at how big it will grow. I have one angel that I got 10 months ago and it is growing like a weed! And in the category of "unasked for advice" - you might want to consider a backdrop for your tank. I see the mini-blinds behind your tank, so it looks like a lot of natural light will be hitting the tank. That could cause you some algae problems down the road. But the tank looks nice!

Rosy Red minnows really need cooler water than the rest of your stock, the maximum for them is more 23-24Celsius.