First, I'd like to welcome you to Tropical Fish Keeping forum. I see you joined this month, and I don't think I've welcomed you yet. Doesn't matter, a second welcome won't hurt.
On the ammonia. Don't know which ammonia detoxifier you used, but most detoxify ammonia by changing it to the less harmful form ammonium. This is basically non-toxic to fish and plants, and in fact plants prefer ammonium as their source of nitrogen. Test kits such as API's read ammonia/ammonium as ammonia, so while it will show ammonia the form is actually ammonium. Not to worry there.
I'd like to know which ammonia product you are using, just in case. And what is the ammonia level in your tap water, is it .25 or something else? May have more when I know these answers.
On the pH. Hardness of the tap water is linked to the pH, the harder the water, the more carbonates it contains, and the more it will "buffer" the pH to prevent it shifting. Efforts to lower it via chemicals--never a good idea anyway--will not work because the buffering capacity of the water will restore the pH and the resulting fluctuating pH is far worse on the fish and can kill them if significant. Your water at 150ppm which equates to about 8 dGH is quite good for most fish. It will buffer the pH a bit, keeping it stable.
The pH will naturally want to lower due to the natural biological processes. Organics (fish waste, uneaten food, any dead plant or fish or snail, dead bacteria, etc) will be broken down by bacteria and as they decompose CO2 is produced and this causes carbonic acid which will lower the pH. The rate at which this occurs is determined by the buffering capacity of the water, the bio load, plants, and bacteria.
My next a question would be why you want to lower it? This obviously depends upon the fish you want to have in the aquarium, and while some require soft slightly acidic water, many are fine with what you have, and some even prefer it. When I know your intended fish, I can comment further on how to change (lower) the pH naturally and safely.
Albino algae eaters. I assume these are the common Chinese Algae Eater which is available in an albino form. I must warn you about this fish. It gets large, 6-8 inches but can reach 12 inches, and as it matures it can become very aggressive to other fish. It also eats less and less algae as it grows. Your tank looks from the photo like perhaps a 10g or 20g, and this fish will outgrow this space in no time, aside from the aggressive issue, causing a real load biologically, they produce a lot of waste. I would return them. You can read more in our profile of the Chinese Algae Eater, click on the shaded name.