I have bred a LOT of angelfish. I know plenty of us here have. I'll try and give you some answers to your questions and advice.
Just some thing to keep in mind for next time, it is usually very obvious which ones are the parents. It only takes a couple minutes of observation if that. They are either fanning the eggs or simply any where near them. They will vigorously and viciously chase away other Angels (among other fish). Many will even attack you when try to remove the eggs.
How old are these fish? How long has it been since they spawned? 50 hatched or 50 eggs? 50 eggs is a very small batch for Angels. 200-400 is the norm. Some are very productive in the 500-600 range. You may have interrupted the mating process, they might just be young or they may have started eating their own eggs before you found them. Black Angels can sometime have smaller batches. I haven't seen that myself, but it is something I have heard it multiple times.
I personally think 85F might be slightly high unless you are working with wild angels. I typically keep them in the 80-85 range, but more toward the 80 side - 80-82. But using cool water to induce breeding is a common trick as pointed out. Not cold water but something cooler then tank water to trigger a temp drop - like 75 in your case. I also do a bigger water change - 25-40% - when I do it. When they get rolling Angels that are well conditioned will breed every 2-3 weeks for a while.
A 50% water change every 4-5 days seems a bit much. If you are using direct tap water it is too much for several reasons. I typically do weekly water changes at around 25% on my tanks. If you don't overfeed, are not trying to quickly grow out fish and don't have an over crowded tank - that's all you really need. And even then more smaller changes are better - like daily 10-15% changes. What kind of filtration do you have?
The pH is a little on the high side but should be fine. If your local guy is really knowledgeable, you have the same (City) water source and well established tanks - he should be able to give you a very good educated guess. It is still only a guess though. I know someone with very hard 8.2 well water that has a pair regularly breeding. I have always kept and bred mine, even wild ones, in 7.6-7.8 pH water. That is high compared to the wild environments but domesticated Angles do fine in it. I am sure someone will correct me if I don't remember this correctly - but most angels in the wild come out of water under 7.4 pH. They go down to around 6.0 for many varieties. I highly recommend you either get a good test kit - not strips - or take your water for testing so you know the pH and other factors. Is it well water or a city water source? Where are you located?
Angles have a mind of their own when it comes to where they will lay their eggs. I have had tanks lined with slate and cones and had them still seek out plants, the filter tube or heater. As I am sure you know, caves of course are one exception - they won't lay them there.
The pleco will most certainly eat any eggs you leave in the tank. Depending on what kind it is they usually do it after lights out because the parents are not as attentive. If you leave the lights on or even a dim light for them, I have found the parents will usually fend off BN and other small plecos.
If you want the parents to raise the fry, it might take a few tries for them to get it right or they might never get it right. I have had fish that knew what to do the first time and I have had others that even after 10 tries ate their own eggs within an hour after laying them. You just don't know what to expect, especially when you don't know the history of your fish. I recommend a separate tank for them when you identify a pair. Parent raised fry seem to be the hardiest to me. They just do better. When looking for maximum hatches with so-so or poor parents though, I would pull them and put them in a small water container with methylene blue so dark you can hardly see the eggs and an air stone next to or over the eggs. I use about 10 times the recommended dosing - it does not hurt them no matter what you have read but definitely helps control fungus. I myself have used the trick for over 10 years and I know others doing it for much longer. There are no
more deformities or any other health issues when you compare them to parent raised fish.
Once they hatch, I move them to a small bare bottom tank with an aged sponge filter. I don't use a direct light on the tank. If it is too bright they have a hard time seeing. Albinos will NOT see and starve to death in well lit tanks, those I try and keep in really dim tanks. Their eye sight is poor and bright light will blind them when they are that small. When fry become free swimming I feed BBS about 3 times a day. You need to keep up on your water changes, the water will foul very quickly especially if you over feed just once. I do changes daily and remove waste and dead BBS. I use an airline to do remove and add water from fry tanks. I use a 5.5 gallon for the first 2 weeks they free swim. Easy to clean and it keeps them dense enough to feed them easily. I have 2-3 hatches of baby brine going during this time. You can also use frozen BBS of Golden Pearls, I have used both but I find live BBS produce the best results by far.
Adult food, I feed primarily flake as well. I use Spectrum and some produced by other hobbyists/small operations. Sometimes I give them a frozen treat. I used to feed occasional live food like CBWs (California Black Worms), daphnia and Mosquito larva.
Just something else to keep in mind. I bred quality angels. I made it a point. There were times I have had 4-5000 going at once, probably many more then you intend to raise. But I got tired of it mostly because even though shops were charging $7-9 for my fish toward the end (and going through them); they didn't want to even give $1 for them. There were stores I would deliver 200-400 to every 2 weeks and experienced no death loss but still didn't think they were worth $1 each or just wanted to give me store credit which I had no need for. Don't get me wrong a couple guys paid me full wholesale list price and were happy to, but most just wanted something for nothing. Now many of them almost never have them and keep asking for them. So be warned about that part of the equation - you need to have somewhere to offload them to at the right time.
--- In firstname.lastname@example.org, Jacob Wojnicki <jakewojnicki@...> wrote:
> I am attempting to breed angelfish. I have had a small bathch of eggs (about 50
> eggs) that I artificially hatched and am now raising. The color on some of them
> is just barely showing. I am trying to get my angelfish to spawn again but they
> seem very reluctant. I have 3 smokey angels, 2 marble angels, and 3 black lace
> angels. I did not see the spawn so I don't know which parents laid the eggs but
> I got them eggs out almost immediately. Therefore I didn't notice which angels
> were really guarding the eggs. I have a smooth piece of slate rock proped
> almost vertical against the tank's wall, a sponge filter, 4 plants, and various
> sizes of flower pots. The pots either upside-down or on their side so they form
> a sort of cave. The last spawn was on the heater. I also have a pleco that I
> am going to be moving very soon. The pleco is about 4 or 5 inches long. Most
> of the angelfish's bodies' are 2 inches tall, excluding the fins. The water is
> about 85 degrees Fahrenheit. I do a large water change of at least 50% every 4
> to 5 days. I have done internet research and talk to a very knowledgeable local
> fish dealer and got mixed results about what the water quality should be. I am
> guessing but am not sure that the water is pretty hard and alkaline and the pH
> is around 8. I feed the fish flake food but am going to start to feed brine
> shrimp and blood worms. I did nothing special for the first spawn with similar
> water conditions and was just feeding flake food. Any adivice on how to get the
> angelfish to spawn would be greatly appreciated. Thank you for your time.
> Jake Wojnicki